Using causal analysis for evaluating environmental and health issues

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1 Using causal analysis for evaluating environmental and health issues Charles Menzie Ph.D Risk Assessment Seminar Series at TERA Center Z

2 What has caused biological impairments in this stream?

3 What has caused the death of these trees?

4 What is happening with the bees?..

5 What is the role of environmental factors on our health?..

6 Who can answer these types of causal questions?

7 Formal causal analysis has been developed to: Provide a technical framework to organize and present evidence Help build a clear weight-of-evidence Help identify causal relationships not otherwise apparent Help prevent lapses of logic

8 Causation Is One of the Most Difficult and Controversial Concepts in Philosophy David Hume Causality is what we experience as associations between events John Stuart Mill Manipulation of a cause results in a change in the effect Karl Pearson Quantify association between variables Ronald Fisher Controlled experiments with replication and randomization Austin Bradford Hill Causality based on strength of evidence Source: Slide courtesy of Glenn Suter, U.S. EPA (2009)

9 Causal Analysis Method to Support Environmental Assessments Problem Statement Identify nature of damage, impairment, risk, and/or contamination List Candidate Causes Develop Conceptual Model of Linkages and Causal Relationships Analyze Evidence Supporting or Refuting Causal Relationships Conduct Additional Analyses to Discriminate Among Causes Guided by evidence criteria Directed at key knowledge gaps No Identify Potential Causes Eliminate based on clear failure of evidence criteria Retain based on strength of evidence Identify additional causes if appropriate based on new information Is information sufficient to identify cause(s)? Yes Report Results of Causal Analyses Use conceptual model to illustrate complete pathways Summarize strength of evidence in relation to criteria Describe basis for sufficiency of evidence Strength of Evidence Criteria Complete causal linkage(s) Strength of association Consistency of association Specificity of the relationship Temporality Gradients of response Plausibility (mechanistic basis) Coherence with facts or theory Experiment analogy Criteria for sufficiency Strength of evidence Degree of remaining uncertainty

10 Example Have air emissions associated with oil and gas extraction damaged crops and desert vegetation?

11 Stands of trees were dying and other effects had been reported

12 Emissions arise from flare stacks

13 And oil burn pits

14 The causal analysis team arrives

15 and goes to work

16 The process began by identifying candidate stressors that could lead to impacts on vegetation

17 Lines of Evidence Were Developed Around Hill s Criteria Co-occurrence Air pollutants, soil conditions, water availability and quality Gradients Distance from sources, spatial variability at local and regional scales Plausible mechanisms Relationship between exposure and effects Consistency of association Literature review and information from other areas Specificity Diagnostic characteristics of plant pathology

18 Model estimates were developed for point/area sources Air Impact Analysis Demonstrated That Alleged Exposures Were Not Occurring

19 GIS was used to examine large-scale patterns. Lack of co-occurrence or gradients of damage for farms

20 Desert Vegetation Was Influenced by Habitat, Not Proximity to Sources Well head Flare pits Wadi Desert vegetation

21 Small-scale Patchiness was Inconsistent with Airrelated Impacts

22 Manifestation of effects were specific to particular causes

23 Soil and biological analyses revealed that there were: Nutrient deficiencies (especially zinc and boron) Salinity impacts (resulting from pumped irrigation) Influences of local fertilization techniques rather than deposition of nitric acid

24 Combinations of Stressors likely Caused the Observed Impacts

25 The second case (USEPA CADDIS): What caused biological impairment in a stream? Learn more about U.S. EPA CADDIS at: Acknowledgment to Dr. Susan Cormier, U.S. EPA

causes Low dissolved oxygen Elevated temperature

26 The Impairment and Candidate Causes Reduced diversity of benthic macroinvertebrates Candidate causes Low dissolved oxygen Elevated temperature Toxicity Sedimentation Altered food quality/quantity High flows

27 Location of Impairment

X X X X Candidate Cause: Asphyxiation Due to Low Dissolved Oxygen Unknown source Farm run-off Site downstream from all farms and most homes had

nutrients Impoundment Deoxygenated hypolimnion Channel modification Reduced riffles Organic enrichment Increased algal growth Release of water

many riffles Decomposition leading to oxygen depletion Biological oxygen demand unchanged from upstream and well below benchmark for effects

28 X X X X Candidate Cause: Asphyxiation Due to Low Dissolved Oxygen Unknown source Farm run-off Site downstream from all farms and most homes had more EPT Total phosphorous, the limiting nutrient in streams, was unchanged compared to upstream Surface run-off, farms and homes Increased nutrients Impoundment Deoxygenated hypolimnion Channel modification Reduced riffles Organic enrichment Increased algal growth Release of water from hypolimnion Lack of aeration Temperature Water released over dam increases aeration Moderately steep gradient and rough substrate causes many riffles Decomposition leading to oxygen depletion Biological oxygen demand unchanged from upstream and well below benchmark for effects Asphyxiation resulting from low dissolved oxygen Loss of invertebrates Dissolved oxygen above levels known to cause mortality for most species of mayflies

X Candidate Cause: Toxicity Associated with Undefined

Ammonia levels greater upstream Episodic exposure Cr Cu

Cr exceeded bench-marks Cu and Cd exceeded benchmarks

Pb, Ni, Zn did not exceed toxic benchmarks Ammonia did

29 X Candidate Cause: Toxicity Associated with Undefined Upstream Source Unknown source Sustained exposure Ammonia levels greater upstream Episodic exposure Cr Cu and Cd Al, Fe, Pb, Ni, and Zn Ammonia Mixture ed. Cr exceeded bench-marks Cu and Cd exceeded benchmarks but unimpaired sites also exceeded benchmarks Al, Fe, Pb, Ni, Zn did not exceed toxic benchmarks Ammonia did not reach toxic levels Death or reproductive failure Loss of invertebrates species

30 Additional Sampling to Delineate Causes MR1 MR2 MR3 MR3

31 Further Investigation Revealed a Episodic Discharge from a Broken Pipe as the Possible Unknown Cause

32 Results from monitoring Biological conditions reach acceptable levels for the state of Connecticut 2.5 years after correction of obvious source of stress

33 The third case: the bees.. Something Is Killing Up To Half Of America's Bees: Whatever's killing honeybees is getting worse, but we still don't know what it is (Popular Science 2013) 8/2013 BEE APOCALYPSE NOW: Scientists discover what s killing the bees and it s worse than you thought.averting beemageddon will be much more difficult than previously thought (Quartz 2013)

34 Declines in Over-Winter Survival Normal colony loss during the winter in the U.S.: ~ 15% Reported by beekeepers to be higher since 2006: ~ 30% Losses were perceived as widespread and substantial During recent years, there has been an increase in use of bees in commercial pollination services

35 Workshop: Causal Analysis of Honey Bee Declines (September 25 27, 2012) Objectives Develop an organized framework to support an objective approach to diagnosing the cause(s) of bee declines using Causal Analysis methodology Rank the most important factors Determine if any factors can be negated Identify critical data gaps Participants 19 experts in honey bee health Experts in causal analysis

36 Developing the Problem Statement What are the causes of the lowered probability of survival (on an annual basis) of productive commercial colonies of honey bees for almond pollination in California dating from approximately 2006 (recognizing preceding conditions)?

37 Stressors Reported to Affect Bees Pests and parasites Varroa mites Tracheal mites Nosema Small hive beetles Wax moths Phorid fly Bacterial diseases American foulbrood European foulbrood Fungal diseases Chalkbrood Stonebrood Viral diseases Cripaviridae Chronic paralysis virus (CPV) Dicistorviridae Acute bee paralysis virus (ABPV or APV) Israel acute paralysis virus (IAPV) Kashmir bee virus (KBV) Black queen cell virus (BQCV) Cloudy wing virus (CWV) Sacbrood virus (SBV) Iflaviridae Deformed wing virus (DWV) Kakugo virus (KV) Varroa destructor virus 1 Iridoviridae Invertebrate iridescent virus type 9 (IIV-6) Dysentery Chilled brood Stress (transportation of hives, etc.) Nutrition Lack of food (habitat loss) Non-diverse food (monoculture) Spoilage of high fructose corn syrup food replacement Pesticides used in agriculture Systemic Spray drift Compounds used in disease treatment (e.g., miticides) Genetics Immune suppression Climate change

38 Honey Bee Life Cycle Stressors

39 Analyze Evidence Supporting or Refuting Causal Relationships Based on Cormier et al. (2010) Time order Co-occurrence Cause-response relationship Sufficiency (lab, field) Interaction Alteration

40 Scoring Strength of Evidence for Causes +++ Convincingly supports ++ Strongly supports + Somewhat supports 0 Neither supports or weakens - Somewhat weakens -- Strongly weakens --- Convincingly weakens NE No evidence

41 Consistency of Evidence Probable cause: Convincing evidence that this cause led to the decline in the survival probability of commercial honey bee colonies in the California almond industry, is impeding the recovery, and may cause further decline and/or continue to impede recovery Possible cause: Some convincing evidence that the cause, acting alone, could contribute to the decline Possible in combination with other factors: Some convincing evidence that the cause, in combination with one or more other causes, could contribute to the decline; weak evidence that the cause, acting alone, can contribute to the decline Unlikely cause: Evidence is too small or runs counter to the criterion that the cause can elicit the decline Indeterminate: Evidence is not available, more information is needed

42 Analysis of Evidence: Process and Results Candidate Stressor Time Order Co-Occurrence (Spatial and Temporal) Sufficiency (lab) Sufficiency (field) Known Mechanism of Action Alteration Conclusions of Consistency of Evidence Viral Diseases ABPV + KBB + IAPV - + +/ Unlikely BQCV + SBV +CBPV +LSV Indeterminate DWV plus other stressors Possible/ contributor IIV-6 CWV VDV1 - Indeterminate Varroa + viruses Probable Bacterial Diseases American foulbrood Unlikely European foulbrood Unlikely Fungal Diseases Chalkbrood Unlikely Nosema apis -/? Unlikely alone/ contributor Etc.

Example of a Probable Cause Varroa destructor plus viruses A mite that feeds on hemolymph of immature bees and adults Mite causes decreased weight and lifespan, severe

43 Example of a Probable Cause Varroa destructor plus viruses A mite that feeds on hemolymph of immature bees and adults Mite causes decreased weight and lifespan, severe malnutrition, malformations, decreased flight duration, reduced sperm production, increased absences, and lower rate of return to hive Mite serves as a vector for viruses

44 Probable Cause Strength of Evidence Varroa destructor plus viruses Time order (+++): Varroa first appeared in the U.S. in 1987; bee viruses considered minor prior to appearance of Varroa Co-occurrence (+++): Varroa not found in Australia; colony losses not significant in South America and Africa where Varroa is well-tolerated Sufficiency/interaction (+++): Lab and field evidence that Varroa can transmit viruses; contagious agent implicated Alteration (+++): Symptoms of reduced colony development, presence of malnourished, deformed, and underweight bees, crawling bees that are unable to fly or that have crippled wings

45 Example of a Possible Cause Nutrition deficiency Bees need carbohydrates (from nectar and honey), protein, minerals, lipids and vitamins (from pollen), and water Nutritional value varies among plants Poor nutrition can affect brood rearing, foraging ability, lifespan, and immunocompetence

46 Possible Cause Strength of Evidence Nutrition deficiency Time order (+): Nutrition deficiency related to monoculture which has increased in recent past Co-occurrence (+): Over-reliance on almonds in California (lack of foraging diversity) Sufficiency/interaction (+): Specificity in response is low because other factors can result in similar responses Alteration (+): Can impair adult survival and immunocompetence but does not translate well into reduced over-winter survival; requires more research to establish a causative link

47 Data Gaps and Recommended Research Likely that multiple causes are involved The number of potential causes and the likelihood that they are interacting complicates research design Additional research on environmental factors and beekeeping practices needed The role of pesticides is being evaluated

48 Final example: building a conceptual model using a human health example cardiovascular disease

49 1. Identify proximal biological mechanisms

50 2. Identify major stressor categories

51 3. Recognize and illustrate relationships among major risk factors

52 4. Identify risk-increasing behaviors

53 5. Identifying other medical conditions that can influence risk

54 6. Include candidate environmental stressors

55 7. Identify risk-reducing factors to inform management actions

56 A resource for learning more

57 Closing comments Causal analysis provides a useful framework There may be multiple causes Information, data quality, and data equity are critically important There is still a need to properly account for and portray uncertainties (ongoing work) The approach can be applied to a wide variety of problems

58 Questions?

- Determining the Causes - Dr. Diana Cox-Foster Pennsylvania State University

Colony Collapse Disorder - Determining the Causes - Dr. Diana Cox-Foster Pennsylvania State University Honey Bees in US Agriculture and the Colony Collapse Disorder Essential for pollination of over 100