BIODEGRADABILITY AND ECOTOXICITY OF PALM STEARIN-BASED METHYL ESTER SULPHONATES

Transcription

1 Journal of Oil Palm Research Vol. 16 No. 1, June BIODEGRADABILITY 2004, p AND ECOTOXICITY OF PALM STEARIN-BASED METHYL ESTER SULPHONATES BIODEGRADABILITY AND ECOTOXICITY OF PALM STEARIN-BASED METHYL ESTER SULPHONATES RAZMAH GHAZALI* and SALMIAH AHMAD* ABSTRACT The biodegradability of palm stearin-based methyl ester sulphonates (MES) was studied and compared with that of linear alkylbenzene sulphonate (LAS). Palm-based MES was readily biodegradable, degrading faster than LAS. The length of its carbon chain affected its biodegradability the longer the chain, the lower the biodegradability. The acute fish toxicity of palm-based MES was determined using Tilapia nilotica (a local fish) and compared with LAS and sodium lauryl sulphate (SLS). The toxicity of MES was found to be comparable to those surfactants. The acute toxicity of MES increased with its carbon chain length. Palmbased MES s biodegradability and acute fish toxicity are comparable to or better than the current high volume anionic surfactants and can provide for their replacement in the future. Keywords: surfactant, MES, biodegradability, acute fish toxicity, environment. Date received: 24 June 2003; Date approved: 1 July 2003; Date revised: 31 December INTRODUCTION The environmental concern over the use of toxic and/or hazardous chemicals is increasing worldwide. There are many such chemicals polluting the environment, with the damage wrought depending on their exposure, persistence in the ecosystem, as well as the characteristics of the affected organisms (Cunningham and Saigo, 1990). Considerable amounts of cleansing materials used in the domestic and industrial domains are directly discharged into waterways. These may pose environmental problems in the waterways including toxicity of the surfactants to microorganisms and fish, foaming, euthrophication and reduction of oxygen transfer into the water that can hinder the self-purification process (Hashim et al., 1992). Therefore, the environmental safety assessment of detergents and related products should primarily focus on the aquatic ecosystem. Ecological evaluation of cleansing products is important for safeguarding the environment. Nowadays, to be accepted worldwide, a product must satisfy rigorous ecological criteria in addition * Malaysian Palm Oil Board, P. O. Box 10620, Kuala Lumpur, Malaysia. razmah@mpob.gov.my to having good performance and a price advantage. Under international law, before a new chemical can be distributed, it must first be registered, for which information on its environmental performance must be supplied. PALM-BASED METHYL ESTER SULPHONATES LAS, alkyl sulphates (AS) and alpha-olefin sulphonates (AOS) are generally used as surfactants in detergents. However, since the two oil crises after the 1970s, detergent manufacturers have shifted their interests to natural oil and fat-based surfactants, for example, MES (Satsuki, 1998). MES is an anionic surfactant derived from natural fats and oils, including palm oil, through sulphonation of fatty acid methyl esters (Masuda et al., 1993). It has good surface-active properties and biodegradability, excellent detergency and is less sensitive to water hardness (Salmiah et al., 1998). At present, however, there are only a few producers of MES worldwide. Due to its excellent detergency, less MES is required in detergents for the same performance than other surfactants (Masuda, 1995). Consequently, the organic load on the environment in the waste 39

2 JOURNAL OF OIL PALM RESEARCH 16 (1) discharged is less. Figure 1 shows the amounts of organic substances discharged per wash for soap, LAS-based detergent and MES-based detergent. The basic performances of these products in aspects such as detergency and foamability are similar, but the differences in surfactant content are considerable. The LAS-detergent contained 38% surfactant while the MES-detergent only 28%. Economic Co-operation and Development (OECD) in its Guidelines for Testing of Chemicals (1992a). A solution, or suspension, of the palm-based MES at 2 mg litre -1 in a mineral medium was inoculated with inoculum (mixed bacterial population) derived from the secondary effluent of a treatment plant treating predominantly domestic sewage and incubated under aerobic conditions in the dark or Figure 1. Total organic loads for soap, linear alkylbenzene sulphonate-based (LAS) and methyl ester sulphonates-based (MES)-detergents. The use of MES in detergents started in the early 1990s in Japan. The evaluation of MES in aquatic ecosystems is therefore important as they are discharged in large volumes into the environment. In this paper, the biodegradability of palm-based MES and its aquatic toxicity to a local fish are evaluated. Materials MATERIALS AND METHODS Palm-based MES used in this study were produced from palm stearin. MES with mixed alkyl chain lengths (C 12 C 18 ) and individual homologues of the MES with 12, 14, 16 and 18 carbons in the alkyl chain were used. They were prepared by sulphonation and neutralization of the corresponding fatty acid methyl esters. The samples were purified to > 80% before use. Conventional surfactants such as LAS (C ) and sodium lauryl sulphate (SLS), with purities > 90%, were used for comparison. Methods Biodegradation test. The test used was the OECD 301D Closed Bottle Test by the Organization for diffuse light at 22 ± 2 o C. Degradation was followed by analysis of dissolved oxygen at four-day intervals using the dissolved oxygen meter over 28 days. The oxygen uptake by the microbial population during biodegradation of the test substance, corrected for uptake by the control run in parallel, was expressed as a percentage of the Theoretical Oxygen Demand (ThOD). A substance is considered readily biodegradable if it is 60% biodegraded in the test period. Acute toxicity test. Aquatic toxicity is the toxicity of a substance towards water organisms. It is assessed by the response of aquatic organisms to the chemical (APHA, 1980). Toxicity tests are part and parcel of the overall evaluation of water pollution as the chemical and physical tests alone are not sufficient to assess the potential effects of the chemical on aquatic biota. The test used was for acute toxicity in static conditions from the OECD Guidelines for Testing of Chemicals (1992b), i.e. OECD 203 Fish, Acute Toxicity Test. Of the seven recommended freshwater fishes, only the common carp (Cyprinos carpio) thrives in tropical freshwater. However, the fish was difficult to obtain in Malaysia, so a local species, Tilapia nilotica, was used instead as it satisfied most of the criteria as a test species (OECD, 1992b; APHA, 1980) - ready availability throughout the year and country, ease of maintenance and convenience for testing. 40

3 BIODEGRADABILITY AND ECOTOXICITY OF PALM STEARIN-BASED METHYL ESTER SULPHONATES The fishes (2-5 cm) were obtained from a local supplier. They were acclimatized for two weeks to the test conditions and fed daily with commercial dry fish food until the day before the test. The fish were not fed during the bioassay but exposed to the test substance at four concentrations in geometric series for 96 hr. The upper and lower concentrations were determined from a range-finding test conducted before this test. The mortalities were recorded at 24, 48, 72 and 96 hr, and the concentrations that killed 50% of the fish, or the LC 50, determined. RESULTS AND DISCUSSION Biodegradation of Palm-Based Methyl Ester Sulphonates (MES) The biodegradation of palm-based MES was faster and higher than that of LAS. The process started quickly and proceeded rapidly in the early stage (Figure 2), reaching the pass level (60% biodegradation) in only five days. The biodegradation of LAS reached the pass level after seven days and the percentage biodegradability is lower than that of MES. The ready biodegradability tests are stringent, providing only a limited time for biodegradation and acclimatization. It may be assumed that a chemical that reaches 60% biodegradation in the test period will rapidly biodegrade in the environment, and is considered to be readily biodegradable (Painter, 1992). Therefore, palm-based MES can be considered a readily biodegradable surfactant. The effect of the carbon chain length (hydrophobic portion) on the biodegradability of MES is shown in Figure 3 by comparing the biodegradabilities of C 12, C 16 and C 18 MES. The longer the chain, the lower was the biodegradability as the microorganisms took longer time to degrade a longer chain and also because of its lower solubility in water. Acute Toxicity of Palm-Based Methyl Ester Sulphonates (MES) The ecotoxicities of LAS and MES on Tilapia were compared to those obtained elsewhere on the recommended fishes (Tables 1 and 2). This was to ensure that the sensitivity of the local species is comparable to those of the standard species. There were only small and non-significant differences between the Tilapia and the other fishes for both the surfactants. The similar results suggest that the Tilapia is as good a test species for the surfactants as the recommended fishes. The toxicity of palm stearin-based MES was compared with two commercial surfactants, LAS and SLS, using Tilapia nilotica as the test species. The ecotoxicity values for the three surfactants are shown in Table 3. The toxicity value for MES was comparable to those for LAS and SLS. The effect of the hydrophobic carbon chain length on the toxicity of MES was also studied (Table 4). Generally, the longer the chain, the higher was the toxicity, except for C 18 MES which toxicity was lower than those of C 14 and C 16 MESs. This was as with most anionic surfactants in which the toxicity increases with the chain length so long as there is sufficient solubility. Figure 2. Biodegradation of palm stearin-based methyl ester sulphonates (MES) and linear alkylbenzene sulphonate (LAS) in the Closed Bottle Test. 41

4 JOURNAL OF OIL PALM RESEARCH 16 (1) Figure 3. Biodegradation of C 12, C 16 and C 18 methyl ester sulphonates (MES). TABLE 1. TOXICITIES OF LINEAR ALKYLBENZENE SULPHONATE (LAS) TO THE TILAPIA AND STANDARD TEST FISHES LAS LC 50 (mg litre -1 ), 96 hr Fish Reference LAS (C ) 11.4 Tilapia nilotica This paper LAS (C ) 12.3 Pimephales promelas ECETOC (1993) LAS (C ) 7.8 Brachydanio rerio Schoberl et al. (1988) 9.2 Carassius auratus LAS (C 11 ) 16.0 Pimephales promelas Greiner and Six (1997) TABLE 2. TOXICITIES OF METHYL ESTER SULPHONATES (MES) TO THE TILAPIA AND STANDARD TEST FISHES MES LC 50 (mg litre -1 ), 96 hr Fish Reference MES (C 14 ) 22.6 Tilapia nilotica This paper (MPOB sample) MES (C 14 ) 24.0 Oryzias latipes Masuda et al. (1994) MES (C 14/16 ) 2.8 Tilapia nilotica This paper (commercial sample) MES (C 14/16 ) 2.4 Oryzias latipes Masuda et al. (1994) TABLE 3. TOXICITIES (LC 50 ) OF C METHYL ESTER SULPHONATES (MES), LINEAR ALKYLBENZENE SULPHONATE (LAS) AND SODIUM LAURYL SULPHATE (SLS) ON TILAPIA Surfactant LC 50 (mg litre 1 )* MES 11.4 Linear alkylbenzene sulphonate (LAS) 11.4 Sodium lauryl sulphate (SLS) 11.6 Note: * Mean values from two tests. 42

5 BIODEGRADABILITY AND ECOTOXICITY OF PALM STEARIN-BASED METHYL ESTER SULPHONATES TABLE 4. TOXICITIES (LC 50 ) OF METHYL ESTER SULPHONATES (MES) WITH DIFFERENT CARBON CHAIN LENGTHS ON TILAPIA MES LC 50 (mg litre 1 ) C C C The acute toxicity of surfactants to fish is not class compound-specific but material- and structurespecific. For anionic surfactants, the aquatic toxicity depends mainly on the length of the carbon chain in the molecule. A certain dependency of the toxicity on the chain length of the alkyl group has been observed in the homologues of AS and alkylbenzene sulphonates (Potokor, 1992; Fendinger et al., 1994) - the longer the carbon chain, the more toxic the anionic surfactant. However, a systematic dependence of the toxicity on the chain length is only recognizable in fully water-soluble compounds. The higher LC 50 (lower toxicity) of C 18 MES may be due to its lower solubility in water. Poorly watersoluble materials present special problems since low solubility masks the toxicity dependence on chain length. CONCLUSION Public concern for the safety of products to the user and environment and for the conservation of natural resources is at an all-time high. Palm stearin-based MES may help to meet the needs for environmental safety. Palm-based MES is a good and cheap active ingredient derived from renewable resources, which can be used in detergent formulations in lieu of the current petrochemical products. Less MES is needed for the same detergency as the conventional surfactants, thus lowering the organic load in wastes discharged to the environment. Palm-based MES is a readily biodegradable surfactant. The biodegradation process of MES started quickly and proceeded rapidly in the early stage, reaching the pass level in only five days. The biodegradability of MES is affected by its carbon chain length (hydrophobic portion). The longer the chain, the lower is the biodegradability. There were only small and non-significant differences in the ecotoxicities of LAS and palmbased MES when tested on Tilapia and the recommended fishes. The sensitivity of the local species is therefore comparable to those of the standard species. The toxicity value for MES was also comparable to those for LAS and SLS. The length of the carbon chain affected the toxicity of palm-based MES where the longer the chain, the higher is the toxicity. Palm stearin-based MES is thus well suited for environmentally friendly detergent due to its good biodegradability and toxicity comparable to the current, high volume anionic surfactants, such as LAS and SLS. The time seems ripe for MES to be used in cleaning products to fulfil the social responsibility of the detergents industry to a cleaner and better environment. ACKNOWLEDGEMENTS The authors would like to thank the Director-General of MPOB for permission to publish this paper, Dr Ma Ah Ngan and Dr Mohtar Yusof for their invaluable comments, and Mr Rosli Yahya for his technical assistance. REFERENCES AMERICAN PUBLIC HEALTH ASSOCIATION (1980). Standard Methods for Examination of Water and Wastewater. Part 800, 15th. Ed. p CUNNINGHAM, P C and SAIGO, B W (1990). Environmental Science, a Global Concern. Wm. C. Brown Publishers, US. p ECETOC (1993). Aquatic toxicity data evaluation. Appendix C: the database. Technical Report No. 56. ECETOC, Brussels. p FENDINGER, N J; VERSTEEG, D J; WEEG, E; DYER, S and RAPAPORT, R A (1994). Environmental behaviour and fate of anionic surfactants. Environmental Chemistry of Lakes and Reservoirs (Baker, L A ed.). American Chemical Society, Washington. p GREINER, P and SIX, E (1997). Evaluation of the results of the LAS-monitoring in Germany. Tenside Surf. Det., 34(4):

6 JOURNAL OF OIL PALM RESEARCH 16 (1) HASHIM, M A; KULANDAI, J and HASSAN, R S (1992). Biodegradability of branched alkylbenzene sulphonates. J. Chem. Tech. Biotechnol., 54: MASUDA, M (1995). Environmental aspects of detergent materials biodegradation of detergent surfactants. Proc. of the 21 st World Congress of the International Society for Fat Research (ISF), Volume 3. PJ Barnes and Associates. p MASUDA, M; ODAKE, H; MIURA, K and OBA, K (1993). Biodegradation of 2-sulphonatofatty acid methyl ester (α-sfme). J. Jpn. Oil Chem. Soc. (YUKAGAKU) 42(9): MASUDA, M; ODAKE, H; MIURA, K and OBA, K (1994). Effects of 2-sulphonatofatty acid methyl ester (α-sfme) on aquatic organisms and activated sludge. J. Jpn. Oil Chem. Soc. (YUKAGAKU) 43(7): ORGANIZATION FOR ECONOMIC COOPERATION AND DEVELOPMENT (1992a). Ready biodegradability. OECD Guidelines for Testing of Chemicals. p ORGANIZATION FOR ECONOMIC COOPERATION AND DEVELOPMENT (1992b). Fish, acute toxicity test. OECD Guideline for Testing of Chemicals. p PAINTER, H A (1992). Detailed review paper on biodegradability testing. OECD Test Guidelines Programme. Periodical review. p POTOKOR, M S (1992). Acute, subacute and chronic toxicity data on anionics. Anionic Surfactants, Biochemistry, Dermatology (Gloxhuber, C and Kunstler, K eds.). 2 nd ed., Surfactant Science Series, 43: SALMIAH AHMAD; ZAHARIAH ISMAIL and JASMIN SAMSI (1998). Palm-based sulphonated methyl esters and soap. J. Oil Palm Research Vol.10 No. 1: SATSUKI, T (1998). Methyl ester sulphonates. New Products and Application in Surfactant Technology. Annual Surfactants Review (Korsa, D R ed.). Volume 1. Sheffield Academic Press Ltd. p SCHOBERL, P; BOCK, K J; MARL and HUBER, L (1988). Data relevant to the ecology of surfactants in detergents and cleaning agents. Report on the State of Discussion in the Study Groups Degradation/Elimination and Bio-testing of the Main Committee Detergents. Copyright of Carl Hanser Verlag, Munich. p