HEALTH RISKS FROM PATHOGENS IN UNTREATED WASTEWATER SLUDGE

Transcription

1 HEALTH RISKS FROM PATHOGE IN UNTREATED WASTEWATER SLUDGE Implications for Australian Sludge Management Guidelines by R. A. GIBBS and G. E. HO SUMMARY Literature concerning pathogen densities in untreated wastewater sludge was reviewed to aid an assessment of the health risks associated with the use of municipal sludge. No information on pathogen densities in Australian sludges was found so risks were assessed using pathogen densities in other countries and infection rates in Western Australia. Based on information from other countries it was estimated that an individual handling sludge and ingesting 0.1 g of sludge would have a greater than 1 OJo chance of becoming infected with Giardia, less than 25% chance of contracting a helminth infection, approximately 1% chance of becoming infected with an enteric virus and less than 1% chance of contracting a Salmonella infection. However a qualitative risk assessment based on reported infection rates in Western Australia suggested that enteric viruses in wastewater sludge pose the most risk followed by Salmonella and Giardia. These risk assessments and a limited amount of epidemiological evidence suggest that digested wastewater sludge is not suitable for unrestricted marketing to the public. Guidelines in the US and UK follow this philosophy. Two issues of concern for Australian sludge guidelines are the use of indicator organisms to predict pathogen densities and the possibility of Salmonella regrowth in composted wastewater sludge. INTRODUCTION The purpose of this review was to assess the potential health risks associated with the use of final sludge from wastewater treatment plants. Sludge products from different plants will vary depending on wastewater and sludge treatments but for assessing the risks this review concentrated on mesophilic anaerobic digested sludge. The effect of sludge treatments on pathogen concentrations was not covered in this review. Two risk assessments were carried out. Firstly the risks were assessed by looking at the following questions. Which groups of people could be at risk from exposure to sludge? What densities of pathogens have been found in wastewater sludge? What is the infectious dose for these pathogens? Therefore what are the risks to exposed people? A separate assessment of risk based on the incidence of disease in Western Australia, estimated excreted loads, persistence of pathogens in the environment and infectious doses was also conducted. These risk assessments were then used to examine possible sludge management strategies and guidelines in Australia. Epidemiological studies were also summarised. It is recognized that the major route of infection for most enteric pathogens is person to person contact. However this does not negate the possibility that exposure to wastewater sludge may be another potential route of infection. PEOPLE AT RISK FROM EXPOSURE TO SLUDGE People at risk from exposure to wastewater sludge can be divided into two groups, those directly exposed and those indirectly exposed (Block, 1986). Directly exposed people might include wastewater and sludge treatment plant workers, sludge transporters and handlers, members of the public using garden products containing sludge, farm workers using sludge and landscaping workers. People directly exposed to wastewater sludge could ingest pathogens contaminating their hands or clothes. Children exposed to sludge are probably most at risk because they are more likely to directly ingest sludge or eat without removing sludge contamination from their hands. Robyn Gibbs is a Research Fellow in Environmental Science at Murdoch University and has eight years experience in water and wastewater microbiology. She is conducting research on the die-off of human pathogens in stored municipal wastewater sludge and sludge applied to land. Goen Ho is Associate Professor in Environmental Engineering at Murdoch University. Since joining the University in 1976 he has carried out teaching and research in the treatment and utilisation of industrial, agricultural and municipal wastes. Indirect exposure to sludge might come from consuming crops grown on sludge-amended soil or consuming meat or water indirectly contaminated from sludge. The following discussion will concentrate on direct exposure to wastewater sludge as there was not enough published information to quantitatively or qualitatively assess the health risks associated with indirect exposure to wastewater sludge. The transmission of pathogens through agricultural application of sewage sludge is therefore not covered in this review but it is an area where more research would be valuable. PATHOGEN DEITIES IN WASTEWATER SLUDGE During an extensive literature search no information about pathogen densities in Australian sludges was found. Work on quantifying pathogens in wastewater sludge in Perth was recently commenced and will be reported separately. A limited number of studies have been carried out in the USA, UK and France and the results are summarised in Table 1. The enteric viruses shown in Table 1 are probably from the enterovirus group which includes poliovirus, echovirus and coxsackieviruses. Other viruses reported by Fradkin eta!. (1985) to be present in wastewater and sludge, but for which no quantifiable densities were found, included rotavirus, hepatitis type A, reovirus, adenovirus and parvovirus. Other bacteria reported to be present were Shigella, enteropathogenic E. coli, Yersinia enterocolitica, Vibrio cholerae and Leptospira. The types of pathogens in Australian sludges should be similar to those from the USA, UK and France. An example of what might be expected in Australian sludges is shown in Table 2 which shows the number of reported cases caused by different pathogens in the Perth metropolitan area and for the whole of Western Australia in Complete data was not available for the whole of Australia so Western Australia was used as an example. Pathogen densities WATER February ,

2 in sludge should reflect the numbers of people in the community infected by enteric pathogens as infected people excrete the pathogen causing the infection. This will vary seasonally and from community to community. Other factors apart from the number of infected individuals will also affect pathogen densities in sludge. Two of these factors are the numbers of pathogens excreted by infected individuals and persistence of these pathogens in the environment. Estimated data for these are shown in Table 2. In the Perth metropolitan area in 1991 there were more reported cases caused by the bacterial pathogens Campylobacter, Clostridium difficile and Salmonella, and the protozoa Giardia than by any other enteric pathogens. The numbers of reported helminth infections were relatively low. Table 1 Summary of Pathogen Densities in Digested Wastewater Sludge Group Viruses Bacteria Pathogen Enteric viruses Salmonella Campy!obacter Protozoa Entamoeba Giardia Helminths Nematodes Ascaris Trichuris Toxocara Toxascaris Cestodes Taenia No. of Organisms/kg* Mean Range SlOt , 1.9xJ04t t Authors Schwartzbrod and Mathieu, 1986 Goyal et a!., 1984 Berg and Berman, 1980 Carriugton et a/., 1991 < Soares eta/., Jewell eta/., 1980 Lue-Hing eta!., 1977 Stern and Farrel, Jones eta/., Fox and Fitzgerald, xl0 4 Sykora eta/., xJOS Soares et a!., 1992 Schwartzbrod et a/., Barbier eta/., 1990 Arther eta/., 1981 Reimers et a/., Fox and Fitzgerald, Barbier eta/., 1990 Arther eta/., 1990 Reimers et a/., Fox and Fitzgerald, Barbier et a/., 1990 Arther eta/., Fox and Fitzgerald, 1977 Reimers eta/., 1986 Arther eta/., Fox and Fitzgerald, 1977 Schwartzbrod et a/., Fox and Fitzgerald, Barbier et a/., 1990 * in some cases converted from numbers/l by assuming that 1 L of sludge weighed 1 kg t not stated :f: converted from number/g dry weight using a dry weight/wet weight ratio of 0.03, geometric mean 950Jo confidence intervals To assess how representative results from Perth were for the rest of Australia the incidences of notifiable enteric diseases in Perth, Melbourne and the Kimberley region of Western Australia were compared. Data was not available for all enteric pathogens but for those shown in Table 3 the incidence of reported enteric infections in Melbourne was approximately half that for Perth. This may have reflected the true incidence but is more likely to have been due to differences in notification rates. The relative infection rates for different pathogens in Perth and Melbourne were similar. The dominant enteric pathogens were Campylobacter, Giardia and Salmonella. Infection rates for notifiable hehninths were low. In the Kimberley region infection rates were considerably higher than in the cities. Giardia was the dominant enteric pathogen. It appears that results from Perth may be representative of other cities but not necessarily of regional areas, particularly northern parts of Australia. If the incidences of enteric infectious diseases in other cities are similar to Perth and Melbourne then Australian municipal sludges would not be expected to contain the high concentrations of helminths shown in other countries. For the helminths Hymenolepis nana, Ascaris lumbricoides and Strongyloides stercora/is, which only have a human host, the numbers of cases and numbers of pathogens excreted by infected individuals in Perth are such that they couldn't give the concentrations shown in other countries unless the number of people with unreported infections is very high. Taenia saginata eggs which originate from infected humans will not infect other people but may present a risk to cattle. Table 2 Number of Persons Infected by Enteric Pathogens in the Perth Metropolitan Area and for the Whole of Western Australia for 1991 (Public Health and Enteric Diseases Unit of State Health Laboratory Services, 1992) and Estimated Excreted Load and Persistence of these Pathogens (Shu val et al., 1986) Group Pathogen No. of Cases Excreted :Wad* Persistencet Metro. State Area Total Viruses Rota virus 259t 10' Adenovirus 206t Enteroviruses 194t J07 3 months Hepatitis A 142t 10' Bacteria Campy/obacter species J07 7 days Salmonella species JOB 2 months Clostridium difjici!e Shigella species J07 I month Aeromonas species Enterotoxigenic E.co/i 0 27 JOB 3 months Protozoa Giardia intestina/is days Blastocystis hominis, Cryptosporidium species Entamoeba species ' 25 days Helminths Hymenolepis nana (dwarf tapeworm) Strongyloides stercora/is weeks Trichuris trichiura (whipworm) ' 9 months Hookworm ova ' 3 months Ascaris lumbricoides (roundworm) I year Taenia saginata 1 I 10' 9 months TYpical number of organisms per gram of faeces t Estimated maximum life of infective stage at 20 to 300C in water, wastewater, soil and on crops :j: Reports from two laboratories (may not be for the whole state), Hargreaves (1992) ~ Pathogen status not established Not stated INFECTIOUS DOSES Infectious dose information is scarce because infectious dose studies depend on human volunteers. There are also problems with using infectious dose information as outlined by Block (1986). Some of these problems are: 1. Infectious doses vary depending on the health of the individual. 2. Infection can be measured in different ways including clinical symptoms, shedding of pathogens in faeces and serological response, so data from different studies may not be comparable. 3. Ingestion of laboratory grown organisms may not replicate ingestion of organisms in environmental samples. Rose and Gerba (1991) and Shuval et al. (1986) summarised infectious doses for different organisms and these are shown in Table 4. In interpreting this data the above limitations need to be kept in mind. Table 4 shows that the probability of becoming infected by consuming one organism is higher for viruses, protozoa and helminths than for bacteria, and the number of organisms required to cause infection in a certain percentage of the population is less for viruses, protozoa and helminths than for bacteria. RISKS FROM EXPOSURE TO FRESH SLUDGE Tables 2 and 4 were used to quantify the health risks of direct exposure to pathogens in wastewater sludge. The risk assessment was based on exposure to fresh sludge rather than treated or stored sludge. Two assumptions were made. Firstly it was assumed that Table 3 Incidence of Enteric Infectious Diseases per Population (1991) Pathogen Incidence/ * Melbournet Perth:j: Kimberley+ Hepatitis A Campylobacter species Giardia species Salmonella species Shigella species Taenia saginata Echinococcus species (hydatid disease) * Population statistics from the Australian Bureau of Statistics, 1988 (Perth and Kimberley) and 1990 (Melbourne) t Infectious Diseases Unit, Health Department Victoria (1992) :j: Public Health and Enteric Diseases Unit of State Health Laboratory Services (1992) 18 WATER February 1993

3 Table 4 Infectious Doses for Enteric Pathogens Pathogen Probability Dose to Cause Incidence of of Infection From Exposure to 10Jo* 1-25'1ot 26-SO'Iot 51-75'1ot 'Iot 1 Organism* Enteroviruses Poliovirus x Poliovirus 3 3.lx Echovirus x Rotavirus 3.lx Norwalk Agent Hepatitis A virus Salmonella species 2.3x Salmonella typhi 3.8x Salmonella newport Salmonella derby Salmonella pullorum Shigella dysenteriae 4.97x1o Shigella flexneri 1x lf Vibrio cholera 7x Escherichia coli (pathogenic) Clostridium perfringens if Campylobader 7x Entamoeba histolytica 2.8x Giardia Iamblia 1.98x Ascaris lumbricoides Ancylostoma duodenale Trichuris trichiura * from Rose and Gerba (1991) t from Shuval et a/. (1986) pathogen densities in Australian sludges are similar to those from other countries. As discussed above this may not be true for helminths. Secondly, for the purposes of estimating the risk, it was assumed that the maximum amount of sludge that any individual would ingest at one time was 1 g and that a more realistic amount that an individual might ingest was 0.1 g. In the worst case it was assumed that Australian sludges contain the maximum numbers of enteric pathogens found in any of the studies from other countries and that an individual handling sludge would ingest 1 g of sludge. The results of this calculation are shown in Table 5. The percentage of individuals likely to become infected with the worst case dose was taken from the infectious dose information given in Table 4, and this is also shown in Table 5. A slightly more realistic infection rate was calculated by assuming that sludge contains the mean number of pathogens shown in Table 4 and that an individual might consume 0.1 g of sludge when handling sludge. This is still likely to be an overestimate as it is unlikely that many people will ingest 0.1 g of sludge. This estimate also does not take into account protozoa and helminth viability. Keeping the assumptions in mind it can be seen from these estimates that for an individual handling sludge and consuming 0.1 g of sludge then there is an approximately 10Jo chance of becoming infected with an enteric virus, less than 1 OJo chance of contracting a Salmonella infection, greater than 1% chance of contracting a Giardia infection and less than 25% chance of contracting a helminth infection. These calculations suggest that if Australian sludges contain the concentrations of enteric pathogens found in digested sludge in the USA, France and UK, then they pose a risk to the health of people handling sludge which has not been treated further than mesophilic anaerobic digestion. The greatest risk appears to arise from Giardia Pathogen Enteric viruses Salmonella Giardia Ascaris Trichuris Table 5 Estimated Infection Rate from Handling Sludge I Wmst Case: Sludge Contains Maximum Number of Pathogens Number in Percentage of 1.0 g Exposed People Infected Jo 2 <1% % % % Average Case: Sludge ~ontains Mean Number of Pathogens Number in Percentage of 0.1 g Exposed People Infected 0.07 <1% to 1% 0.04 <1% 1.0 >1% 0.4 <25% 0.22 <25% and helminths in sludge. In Australian municipal sludges the risks from helminths should not be as great but risks of Giardia infections may be similar. A qualitative risk assessment was also carried out. Rather than using data from other countries the assessment was based on reported infection rates in Western Australia. This was used in conjunction with estimated excreted loads and persistence of pathogens in the environment as shown in Table 2. Some of the pathogens shown in Table 2 were not included in the qualitative risk assessment. Taenia saginata was excluded because it is not transmitted directly from person to person but needs an intermediate host. Clostridium difficile was not considered to present a risk from faecal-oral transmission. Blastocystis hom in is is not a clearly established pathogen. Ascaris lumbricoides was considered to present a negligible risk relative to the other pathogens because of the low number of cases in Western Australia. Information in Table 2 was classified into low, medium or high as outlined in Table 6. Infectious dose classifications were taken from Shuval et al. (1986). The classifications were then combined to rank the pathogens into groups. Group 5 contains the pathogens which presented the most risk with the risks decreasing to group 1 which contains the pathogens of least risk. The classifications and groups of pathogens are shown in Table 7. Table 6 Criteria Used to Classify Number of Cases in Western Australia, Excreted Load and Pathogen Persistence Classification No. of Cases Excreted Load Persistence Low less than and less 1 month and less Medium 100 to and 10 5 greater than 1 month to 3 months High greater than 500 greater than 10 5 greater than 3 months This risk assessment is obviously very general and based on a number of assumptions. Some of the assumptions were that: 1. Each of the different factors had equal weight (number of cases, excreted load, persistence and infectious dose). 2. Reported cases reflected symptomless and unreported cases. 3. Input into wastewater from infected animal waste was not significant. 4. Where data was not available it was estimated from data for similar pathogens. 5. Any pathogen which resulted in less than 2 cases per people per year was considered to present negligible health risk in wastewater sludge. 6. Levels of immunity to viruses were not significantly higher than for other pathogens. 7. Salmonella regrowth potential was not significant. Based on the qualitative risk assessment and with these assumptions in mind then the pathogens of most concern in Western Australian sludges are enteric viruses. The next group of pathogens which are of concern are Salmonella, Giardia intestinalis and Trichuris trichiura. Most of the Trichuris trichiura infections were Group Group 5 (highest risk) Group 4 Group 3 Group 2 Table 7 Relative Health Risks of Different Groups of Pathogens Pathogen Rotavirus Adenovirus Enterovirus Hepatitis A &zlmonella Giardia intestinalis Trichuris trichiura Campylobacter Shigella Cryptosporidium Hookworm ova Hymenolepis nana Entamoeba Strongyloides stercora/is Enterotoxigenic EColi Group 1 (negligible risk) Ascaris lumbricoides No. of Cases Excreted Persistence Infectious in Western Load Dose Australia in 1991 high high medium high high medium low low medium low high low high high low high medium high low medium medium medium low low medium low medium low medium low low low low medium low low medium low low low low high medium high WATER February

4 associated with travellers and recent immigrants so infection rates in the resident population appear to be low. This organism was therefore not considered to present a major risk from transmission through sludge. Most of the hookworm, Hymenolepis nana and Strongyloides stercora/is infections reported in Western Australia were from patients in the Kimberley region. The risk of infection from helminths in Perth sludges would therefore appear to be low. This may be similar in other southern cities in Australia. In northern Australia the risk of contracting helminth infections through contact with sludge may be higher. The qualitative risk assessment using infection rates in Western Australia gave a different result to the quantitative risk assessment based on pathogen densities in sludge in other countries. The quantitative risk assessment suggested that Giardia and helminths presented more of a risk than enteric viruses and Salmonella. One reason for the differences may be that poor recoveries of pathogens in sludge resulted in an underestimation of pathogen densities in sludge in other countries. Measured enteric virus concentrations in sludge may have been particularly low. Another reason is that methods used to detect Giardia did not assess viability. However the differences may also underline the general uncertainty attached to the results due to the assumptions made and lack of data which could be used in the risk assessment. The conclusions of the qualitative risk assessment differ from those of Shuval et at. (1986). They proposed a model to predict the relative infectiveness of pathogens in causing infections through wastewater irrigation in developing countries. The risks from pathogens were ranked in the following way. 1. High 2. Lower Helminths Bacterial infections Protozoan infections 3. Least Viral infections. In contrast the ranking developed in this study (shown in Table 7) suggested that viruses present the highest risk, followed by bacteria and protozoa with helminths presenting the least risk. There are probably two main reasons for the difference which are due to the Shu val et al. (1986) model being developed for developing countries. Firstly Shu valet a!. (1986) assumed that the prevalence of helminth infections was very high. Shuval et a!. (1986) used figures of 60o/o prevalence for both Ascaris and Trichuris. Based on reported cases then the prevalence of Ascaris and Trichuris in the Perth metropolitan area in 1991 was and 0.01% respectively (Public Health and Enteric Diseases Unit of State Health Laboratory Services, 1992). The second reason is that Shuval et a!. (1986) assumed that due to poor hygiene most infants would be exposed to enteric viruses and subsequently immune to enteric virus infections. This assumption was not made for this study so immunity was not treated as a significant factor in the risk assessment. EPIDEMIOLOGY Epidemiological studies are another way of assessing the risks from pathogens in sludge. However epidemiological information is limited because the costs involved in epidemiological studies are extremely high. In studies described by Jakubowski (1986) costs ranged from US$ to US$ for retrospective studies, and US$ to US$ for prospective studies. These studies were carried out in the late 1970s and early 1980s. There are a greater number of studies involving exposure to wastewater and these were summarised by Shuval eta!. (1986). Block (1986) could report only four epidemiological studies of exposure to sludge rather than exposure to wastewater. One of these was a study of sludge compost workers described by Clark et a!. (1984). Workers directly involved in composting showed evidence of an immune response to antigens which was higher than groups not involved with compost activities. More symptoms of burning eyes and skin irritation were also reported among compost workers. However these may have been associated with high dust levels rather than the sludge. Jakubowski (1986) described an epidemiological study of farm residents on farms with anaerobically digested sludge spread on their fields. No significant differences were observed between the test and control groups for reported illness and serology. The author noted that health risks might have been higher with a higher rate of exposure. Another study described by Block (1986) reported hepatitis A infections in four men who spread wastewater sludge on farmland. It is probable that the men were infected during the course of their work. In a review of the epidemiology of Salmonella, Pike (1986) found only one published outbreak of salmonellosis which involved the use of sludge. This involved 98 human cases drinking unpasteurised milk from a farm in Scotland. Sludge containing effluent from a chicken factory had been sprayed on grassland and cattle reintroduced shortly afterwards. Cows, calves and domestic pets were found to be infected with S. typhimurium. Another milk-borne epidemic in Czechoslovakia (Raska et al. 1966) appeared to have been caused by sludge spread on land. Cesspool wastewater was spread on fields and this resulted in contamination of the water supply into a dairy. This appeared to lead to contamination of the milk and an infectious hepatitis A epidemic. In 1986 European Community round table discussions were held on the risks associated with the agricultural use of wastewater sludge (EC Panel, 1986). A Salmonella panel stated that wastewater and wastewater sludge were the source of infection in 12 reported outbreaks of salmonellosis. How many of these outbreaks were actually associated with municipal wastewater sludge is not clear. At least three of them which occurred in the UK were associated with animal wastes, wastewater or septic tanks rather than municipal sludge. The conclusions of the panel were that sludge presented a hazard to the health of animals and men and that it should be treated to destroy pathogens or restrictions imposed on the use of land after sludge was applied. A parasite panel agreed that sludge spread on land can act as a vector of Ascaris and Taenia saginata. A virus panel concluded that there were only two relevant reports of wastewater sludge acting as a source of infection for the spread of enteric viruses. These were the two hepatitis A outbreaks described above. On the basis of the limited number of studies that have been carried out it appears that human infection has occurred through handling sludge or the use of wastewater sludge in agriculture. However if guidelines are followed which include sludge treatment or restrictions on the use of sludge-amended soil and public access, then the health risks appear to be low. SLUDGE GUIDELINES A number of countries have guidelines for the use of wastewater sludge on land but the formulation of guidelines is a difficult process because there is very little information available. As shown above epidemiology has not provided enough information to state conclusively whether past sludge management practices have resulted in any disease in exposed humans. There does seem to be some evidence that wastewater sludge has been associated with a few cases of infection, but not in cases where the sludge had been treated or where use restrictions were imposed after sludge was applied to land. Studies in the USA, France and UK have demonstrated that sludge which has not been treated past mesophilic anaerobic digestion may contain pathogenic viruses, bacteria, protozoa and helminths. Estimated infection rates among exposed populations consuming 0.1 g of sludge were approximately 1% for enteric viruses, < 1% for pathogenic bacteria, > 1% for Giardia and < 25% for helminth ova. The epidemiological information and reported pathogen densities from other countries therefore suggest that sludge which has only been treated by mesophilic anaerobic digestion is not safe for unrestricted use by the public. Legislators in other countries have adopted this philosophy and responded to it in two ways. The first is by requiring that sludge undergo further sludge treatment before unrestricted use. The second is by imposing restrictions on the use of partially treated sludge. These restrictions include requirements such as subsurface injection or tilling of sludge into soil, limitations on access and withholding periods for sludge amended soil. There are differences between the guidelines in different countries and this is illustrated by examining the US and UK guidelines. Sludge guidelines in the USA are in the process of change so there are present guidelines (US EPA, 1989a) and proposed new regulations (US EPA, 1989b ). The proposed regulations may be modified again and were expected to be promulgated towards the end of There are differences between the US and UK guidelines (DOE, 1989) in three major areas. The first difference is in the way that sludge is classified. In the UK sludge is classified as treated or untreated and in the US sludge is classified as untreated, treated by a process to significantly reduce pathogens (PSRP) or treated by a process to further reduce pathogens (PFRP). The second difference is between the restrictions placed on the use of the different classifications of sludge. The US allows the unrestricted use of sludge which has been treated by a 20 WATER February 1993

5 ~ ~ process to further reduce pathogens such as composting. The UK does not seem to allow the unrestricted marketing of any type of sludge. In the UK untreated sludge can be used in agriculture with associated use restrictions. The US does not allow the use of untreated sludge in agriculture. The third difference is between the monitoring and classification requirements. Sludge guidelines in the UK specify acceptable sludge disposal practices with land use restrictions but do not require any monitoring for pathogens or indicator organisms. The present US 40 CFR Part 257 guidelines are also based on acceptable processes and procedures. However the new US proposed regulations have requirements which specify acceptable pathogen densities, but also specify alternative process plus indicator organism density requirements. IMPLICATIO FOR AUSTRALIAN GUIDELINES Australia is in the process of formulating guidelines for sludge management. These guidelines are not yet available for public comment so the details are not discussed here. However the following discussion concerns issues which may be raised in the guidelines. Pathogens of Concern The qualitative risk assessment based on the incidence of disease in Western Australia (Table 2) produced a ranking of the relative risks of different pathogens in wastewater sludge (Table 7). Enteric viruses were considered to present the greatest health risk in wastewater sludge. Also of concern were Salmonella and Giardia. Pathogens such as Campylobacter, Shigella and Cryptosporidium presented a lower risk. The risk of infection from helminths in municipal sludge was considered to be low. Indicator Organisms as Predictors of Pathogen Densities in Wastewater Sludge After assessing the use of indicator bacteria for predicting pathogen densities in sludge Pederson (1981) and Lewis-Jones and Winkler (1991) did not recommend the use of indicator organisms. Pederson (1981) evaluated the available literature and concluded that no single indicator organism maintained a density level which was constant relative to that of pathogenic organisms. In a later review Lewis-Jones and Winkler (1991) concluded that several microorganisms in raw and treated sludges could be used as indicators of other organisms but the true extent of sludge contamination could only be assessed by direct determination of the relevant organisms. Berg and Berman (1980) studied the effect of anaerobic digestion on viruses and indicator bacteria indigenous to domestic sludges. They found that indicator bacteria were destroyed more rapidly than viruses and large variations in the numbers of viruses occurred over narrow ranges of faecal coliforms, total coliforms and faecal streptococci. The rates of destruction of faecal streptococci by digestion were closest to those of virus destruction so they concluded that faecal streptococci may by useful process indicators. Lewis-Jones and Winkler (1991) came to a similar conclusion. They described a study which examined the relationship between enteroviruses, Salmonella, coliforms, faecal streptococci and frna phages in raw and treated sludges. Faecal streptococci appeared to be reliable indicators of virus contamination. A significant correlation between Salmonella and viruses suggested that Salmonella could also be used as a virus indicator but frna phages and coliforms were not good indicators of enteric viruses. In contrast to the results for viruses, Lewis-Jones and Winkler (1991) found that faecal streptococci were not good indicators for Salmonella as their susceptibility to sludge treatments varied. Yanko (1988) found that there were significant correlations between Salmonella and total coliforms, faecal coliforms and faecal streptococci. Linear regression was used to predict that Salmonella were below the detection limit ( < 0.2/g) when indicator concentrations were below 240 MPN/g, 43 MPN/g and 73 MPN/g for total coliforms, faecal coliforms and faecal streptococci respectively. These studies indicate that faecal streptococci may be useful indicators of enteric virus densities in sludges. Faecal and total coliforms did not appear to be good indicators which suggests that E. coli may also be a poor indicator. However the results were not conclusive. No studies were found which examined the relationship between faecal indicators and parasites. This is an area where more information is needed as the risk assessment suggested that Giardia may be a pathogen of major concern in sludge. T~~ reviewed s~u~ies do not pr?vide any basis for using the dens1t1es of faecal m~1cator bactena m sludge to predict the presence or absence of entenc pathogens. Salmonella Regrowth in Composted Wastewater Sludge In the US, sludge which has been treated by a PFRP process can be marketed without restrictions. Acceptable PFRP processes are composting, heat drying, heat treatment, thermophilic aerobic digestion, beta ray irradiation, gamma ray irradiation and pasteurization (US EPA, 1989a). Laboratory studies have demonstrated that Salmonella can regrow in composted wastewater sludge (Russ and Yanko 1981). The results of a field study also suggest this (Yanko 1988). In the field study the finished product from a windrow com posting facility contained very few Salmonella but blended compost products contained high levels of Salmonella. The authors measured Salmonella levels in the other blending products and concluded that nutrient related regrowth of Salmonella was the only explanation for these high levels. In the described study Salmonella was regularly detected in composted sludge meeting PFRP criteria. Mixing with other products and bagging seemed to be conditions which favoured regrowth. These studies suggest that some com posted sludges have the potential to support Salmonella regrowth. Composted sludge may appear Salmonella free but contain low levels of Salmonella which can grow after bagging. As recommended by Yanko (1988) additional research to better understand what conditions give rise to Sa!tizonella regrowth is warranted. Management practices may significantly alleviate any potential hazards associated with Salmonella in compost. Yanko (1988) also discussed the results of two studies which suggested that seeded laboratory cultures of Salmonella may not predict the regrowth of indigenous Salmonella. This study raises questions about what form of monitoring could adequately assess and prevent the marketing of sludge products with unacceptably high densities of Salmonella. A laboratory test of regrowth potential may not be an adequate predictive tool. I CONCLUSIO An epidemiological review and assessment of the health risks associated with municipal wastewater sludge suggested that untreated digested sludges are not suitable for unrestricted marketing to the public due to unacceptably high risks associated with enteric viruses, Salmonella, Giardia and some helminths. However both epidemiological information and studies of pathogen concentrations in sludge were scarce. The risk assessment was based on data from other countries so a qualitative risk assessment based on reported cases in Western Australia was carried out. This suggested that enteric viruses in sludge present the greatest risk followed by Salmonella and Giardia. Two issues are of concern for Australian guidelines. Firstly the use of faecal indicator bacteria to predict pathogen densities in sludge was not supported by the literature. Secondly the regrowth potential of sludge treated by com posting or other forms of further treatment needs further discussion. Research in these two areas would be of benefit. ACKNOWLEDGMENTS The review documented here was part of a project funded by the Water Authority of Western Australia and Urban Water Research Association of Australia. Members of the steering committee for this project were Mr Hugh Rule, Mr Ivan Unkovich and Dr Richard Lugg. The opinions expressed here are those of the authors and do not necessarily reflect those of the steering committee, Water Authority of Western Australia or Urban Water Research Association of Australia. REFERENCES Arther R.G., Fitzgerald P.R. and Fox J.C. {1981). Parasite ova in anaerobically digested sludge. Journal of the Water Pollution Control Federation, 53(8), Barbier D., Perrine D., Duhamel G., Doublet R. and Georges P. {1990). Parasitic hazard with sewage sludge applied to land. Applied and Environmental Microbiology, 56(5), Berg G. and Berman D. (1980). Destruction by anaerobic mesophilic and thermophilic digestion of viruses and indicator bacteria indigenous to domestic sludges. Applied and Environmental Microbiology, 39(2), Block J.C. (1986). Biological Health Risks of Sludge Disposal. In Epidemiological Studies of Risks Associated With the Agricultural Use of Sewage Sludge: Knowledge and Needs. Ed. by J.C. Block, A. H. Havelaar and P. L'Hermite, Elsevier Applied Science Publishers, London and New York. Carrington E.G., Pike E.B., Auty D. and Morris R. (1991). Destruction offaecal bacteria, enteroviruses and ova of parasites in wastewater sludge by aerobic thermophilic and anaerobic mesophilic digestion. Water Science and Technology, 24(2), WATER February

6 Clark C.S., Bjornson H.S., Schwartz-Fulton J., Holland J.W. and Gartside P.S. (1984). Biological health risks associated with the com posting of wastewater treatment plant sludge. Journal of the Water Pollution Control Federation, 56(12), DOE (1989). Code of Practice for Agricultural Use of Sewage Sludge. HMSO, London. EC Panel (1986). Conclusions and recommendations from panel discussions. In Epidemiological Studies of Risks Associated With the Agricultural Use of Sewage Sludge: Knowledge and Needs. Ed. by J.C. Block, A. H. Havelaar and P. L'Hermite, Elsevier Applied Science Publishers, London and New York. Fox J.C. and Fitzgerald P.R. (1977). Parasite content of municipal wastes from the Chicago area. Journal of Parasitology, 63, Fradkin L., Lutkenhoff S., Stara J., Lomnitz E. and Cornaby B. (1985). Feasibility for performing a risk assessment on pathogens. Journal of the Water Pollution Control Federation, 57(12), Goyal S.M., Schaub S.A., Welliogs F.M., Berman D., Glass J.S., Hurst C.J., Braesher D.A., Sorber C.A., Moore B. E., Bitton G., Gibbs P.H. and Farrah S.R. (1984). Round robin investigation of methods for recovering human enteric viruses from sludge. Applied and Environmental Microbiology, 48(3), Hargreaves J. (1992). Annual report of the CDI 'Viruses' reporting scheme, Communicable Diseases Intelligence, 16(10), Infectious Diseases Unit, Health Department Victoria. (1992). Surveillance of Notifiable Infectious Diseases in Victoria. Health Department Victoria. ISSN Jakubowski W. (1986). US EPA sponsored epidemiological studies of health effects associated with the treatment and disposal of wastewater and sewage sludge. In Epidemiological Studies of Risks Associated With the Agricultural Use of Sewage Sludge: Knowledge and Needs. Ed. by J.C. Block, A.H. Havelaar and P. L'Hermite, Elsevier Applied Science Publishers, London and New York. Jewell W.J., Kabrick R.M and Spega J.A. (1980). Autoheated Aerobic Thermophilic Digestion with Air Aeration. US EPA, Cincinnati, Ohio. R Jones K., Betaieb M. and Telford D.R. (1990). Seasonal variation of thermophilic campylobacters in sewage sludge. Journal of Applied Bacteriology, 69, Lewis-Jones R. and Winkler M. (1991). Sludge Parasites and Other Pathogens. Ellis Horwood, London, Sydney. Lue-Hing C., Sedita S.J. and Rao K.C. (1977). Viral and Bacterial Levels Resulting From the Land Application of Digested Sludge. Report No Metropolitan Sanitary District of Greater Chicago. Pederson D.C. (1981). Density Levels of Pathogenic Organisms in Municipal Wastewater Sludge- A Literature Review. US EPA, Cincinnati, Ohio. EPA- 6001S Pike E.B. (1986). Recent UK research on incidence, transmission and control of Salmonella and parasitic ova in sludge. In Epidemiological Studies of Risks Associated With the Agricultural Use of Sewage Sludge: Knowledge and Needs. Ed. by J.C. Block, A.H. Havelaar and P. L'Hermite, Elsevier Applied Science Publishers, London and New York. Public Health and Enteric Diseases Unit of State Health Laboratory Services (1992). Western Australian 1991 enteric pathogen report. Communicable Diseases Intelligence, 16(8), Raska K., Helcl J., Jezek J., Kubelka Z., Litov M., Novak D., Radkovsky J., Sery V., Zejdl J. and Zikmud V. (1966). A milk-borne infectious hepatitis epidemic. Journal of Hygiene, Epidemiology, Microbiology and Immunology, 10, RIVER MURRAY SALINITY MITIGATION SCHEMES IN SOUTH AUSTRALIA by R J Newman We apologise to both the author and readers for the transposition of the captions on page 25, and the occlusion of the 'continuation from page 26 to page 36'. The graph labelled Fig. 4 should have the caption Fig. 2. The diagram labelled Fig. 2 should have the caption Fig. 3. The map labelled Fig. 3 should have the caption Fig. 4. The following References have been added to the paper. REFERENCES Collingham.E.B. (1986), ~oolpunda Groundwater Interception Scheme; Geotechmcal Report for disposal (of salme groundwater) to a basin at Stockyard Plain. EWS Dept Collett A. (1987), Woolpunda Groundwater Interception Scheme Report on River Flow and Salinity studies, EWS Dept 87 I 45. ' Kinhill Engineers (1987), Woolpunda Groundwater Interception Scheme, Draft Envuonmental Impact Assessment. Murray-Darling Basin Ministerial Council (1988), Draft Salinity and Drainage Strategy, Discussion paper No. I. Newma1_1 R.J. (1987), Woolpunda Groundwater Interception Scheme; Project Design Report, EWD Dept 87 I 46. Social & Ecological Assessments (1989), Waikerie Salt Interception Scheme, Public Environmental Report. Telfer A. (1987), Woolpunda Groundwater Interception Scheme; Hydrogeology - Executive Summary. EWS Dept 87 I 42. Telfer A. (1989), Waikerie Salt Interception Scheme; Final design report Hydrogeology. EWS Dept ' Reimers R.S., McDonnel D.B., Little M.D., Bowmann D.O., Englande A.J. and Henriques W.O. (1986). Effectiveness of wastewater sludge treatment processes to inactivate parasites. Water Science and Technology, 18, Rose J.B. and Gerba C.P. (1991). Assessing potential health risks from viruses and parasites in reclaimed water in Arizona and Florida, USA. Water Science and Technology, 23, Russ C.F. and Yanko W.A. (1981). Factors affecting salmonellae repopulation in composted sludges. Applied and Environmental Microbiology, 41, Schwartzbrod L. and Mathieu L. (1986). Virus recovery from wastewater treatment plant sludges. Water Research, 20(8), Schwartzbrod J., Mathieu C., Thevenot M.T., Baradel J.M. and Schwartzbrod L. (1987). Wastewater sludge: Parasitological and virological contamination. Water Science and Technology, 19(8), Shuval H.I., AdinA., Fattal B., Rawitz E. and Yekutiel P. (1986). Wastewater Irrigation in Developing Countries, Health Effects and Technical Solutions. World Bank Technical Paper Number 51, The World Bank, Washington D.C. Soares A.C., Gerba C.P., Josephson K.L and Pepper I.L. (1992). Effect of anaerobic digestion on the occurrence of enteroviruses, Giardia cysts and indicator bacteria in sewage sludge. Presented at IAWPRC Conference, Washington D.C., May. Stern G. and Farrell J.B. (1977). Sludge disinfection techniques. In Proc. of Nat. Conf on Composting of Municipal Residues and Sludges, Washington D.C. Information Transfer, Inc., Rockville, MD. Sykora J.L., Sorber C.A., Jakubowski W., Casson L.W., Cavaghan P., Shapiro M.A. and Schott M.J. (1991). Distribution of Giardia cysts in wastewater. Water Science and Technology, 24(2), US Environmental Protection Agency (1989a). Control of Pathogens in Municipal Wastewater Sludge for Land Application Under 40 CFR Part 257. US EPA, Cincinnati, Ohio. EPAI US Environmental Protection Agency (1989b). Standards for the disposal of sewage sludge: Proposed rule. Federal Register, 54, Yanko W.A. (1988). Occurrence of Pathogens in Distribution and Marketing Municipal Sludges. US EPA, Cincinnati, Ohio. EPAI6001!-8710!4. AWWA-WMAA 2nd NATIONAL HAZARDOUS AND SOLID WASTE CONVENTION ACHIEVEMENTS AND CHALLENGES Melbourne May 8-11, 1994 CALL FOR PAPERS Technical Program The technical program will focus on achievements and case studies, and the problems and challenges that remain. Abstracts are requested which address the following key issues relating to industrial, commercial and municipal wastes: Hazardous Waste Solid Waste Waste minimisation, recycling, Waste minimisation clean technology Recyling Treatment and disposal - marketing, economics, technologies collection, - biological treatment sorting - options to incineration Resources recovery - problem wastes - materials and energy - emerging technologies Landfill sifting and operation Control of air emissions Pricing - collection, disposal Regulations issues Obtaining environmental Contaminated Land approval Risk assessment and site-specific Community involvement solutions Government - regulations and Clean-up technologies role Environmental auditing Typewritten abstracts, not exceeding 250 words, of proposed papers to be presented verbally or in poster session, must be received by the Convention Secretariat by 31 May Abstract submittal forms available from Secretariat. Abstract submittal Selected papers will be notified Final manuscripts by Deadlines 31 May August December 1993 Convention Secretariat 2nd National Hazardous & Solid Waste Convention Secretariat PO Box 388, Artarmon W 2064 Telephone (02) Facsimile (02) Aquatic and Environment Chemistry Articles Wanted for August Supplement The August 1993 issues of Water and Chemistry in Australia will contain a joint supplement using the successful format of the August 1992 supplement. The editors are seeking articles and short items. Article titles and a short summary should be submitted by April 1 to Bob Swinton (phone-fax (03) ) or Bruce Guise ph (052) Fax (052) For advertising, contact the AWWA Federal Secretariat. 22 WATER February 1993