Methylmercury Exposure through Fish Ingestion and Trends in Human Health Risk in the Merrimack River Watershed A thesis submitted by Tiffany A. Blake in partial fulfillment of the requirements for the degree of Master of Science in Civil and Environmental Engineering Tufts University August 2017 Advisers: Anne Marie C. Desmarais, David M. Gute, Diane M. Manganaro ABSTRACT Northeast Massachusetts has the highest concentration of point sources for mercury emissions in the state. Emissions from major point sources decreased 96% from the 1990s to 2008 as a result of stricter controls on releases. Fish consumption is the primary exposure route for people. This thesis used risk assessment to assess whether reduction in mercury emissions over time was contributing to lower exposure and risk among people who eat fish from lakes and ponds in the Merrimack River watershed. Decreases in risk were observed from 1999 to 2011, but this risk assessment demonstrates that unacceptable risk continues to exist for people who eat fish from these water bodies, especially young children. Small sample sizes and differences in average fish weight throughout the study period introduced uncertainty in the study. The observed reduced risk has positive public health implications but also demonstrates the continuing need for fish advisories. ii ACKNOWLEDGEMENTS I would like to express great thanks to my committee members: Anne Marie Desmarais, David Gute, and Diane Manganaro for their continuous guidance throughout this entire process. With special thanks to my advisor Anne Marie, who served as my editor, mentor, and inspiration throughout my graduate studies. I thank Carolyn Talmadge, Tufts GIS Specialist, and Karen Vagts, Tufts Librarian, for lending me their expertise. I also thank my family (special thanks to my mother and Christopher, for shuttling me around and always lending an ear), my grandparents (Pop and my inspirational “Tufts grad” Nana), my friends, and my Pj for their unfaltering love and support. I would like to dedicate my work to you. I would also like to dedicate this work in memory of my loved ones that are no longer with us: to my grandparents (Nene and Papa); a special thank you to my Uncle Bob, who spent hours talking with me as I was beginning this journey. I love you all, always. Thank you to my undergraduate advisor, Joel, who encouraged me to apply to Tufts. Thank you to my boss and newest mentor, Glen, for being understanding, accommodating, and believing in me. Lastly, I thank my mentors who have shared both scientific expertise and friendship: Peter, Carol, and Nina. With special thanks to Nina, who gave me a chance that I will never forget… I promise to pay it forward someday. Thank you Tufts University Civil and Environmental Engineering Department, both students and faculty, for continuing to fuel my passion of environmental health. May this passion and enjoyment never falter as I build my career to protect all beings, and most importantly, our Earth: without which life would cease to exist. iii TABLE OF CONTENTS ABSTRACT……………………………………………………………………...ii ACKNOWLEDGEMENTS…………………………………………………….iii 1.0 INTRODUCTION…………………………………………………………...1 2.0 BACKGROUND……………………………………………………………..4 2.1 Mercury in the Environment…………………………………………..5 2.2 Mercury in Environmental Media……………………………………..7 2.2.1 Atmospheric…………………………………………………7 2.2.2 Water..…………………………………………………….....8 2.2.3 Soil…………………………………………………………..9 2.3 Bioconcentration and Biomagnification……………………………..10 2.4 Sources of Human Exposure to Mercury…………………………….11 2.5 Health Effects and Toxicology of Mercury in Humans……………...12 Health Effects…………………………………………………….12 Absorption and Distribution……………………………………..13 Metabolism……………………………………………………….13 Excretion………………………………………………………....14 2.6 Risk Assessment and Dose-Response Variables…………………….14 2.6.1 Dose-Response Variables………………………………….15 2.7 Methylmercury Epidemiological Studies Used to Derive Dose- Response Values…………………………………………………………16 Faroe Islands and the EPA Reference Dose for Chronic Oral Exposure (RfD)…………………………………………………..18 Seychelles Child Development Study and the ATSDR Minimal Risk Level (MRL)……………………………………...………………19 2.8 Health Benefits of Fish Consumption vs. Mercury Exposure……….21 2.9 Risk with Consuming Freshwater Fish vs. All Fish…………………24 2.10 Fish Consumption Studies………………………………………….25 2.11 Massachusetts Fish Consumption Advisories for Mercury in Freshwater Fish……………………..……………………………………26 2.12 Massachusetts Regulations…………………………………………27 Mercury Added Products………………………………………...27 Emissions………………………………………………………...28 2.13 Massachusetts Fish-Tissue Mercury Reductions…………………...30 3.0 METHODOLOGY…………………………………………………………32 3.1 Study Methods……………………………………………………….32 3.2 Fish Mercury Data…………………………………………………...32 3.2.1 Merrimack River Watershed……………………………….33 Municipal Solid Waste Combustors……………………...33 Regulatory Initiatives…………………………………….34 iv Fish Tissue Monitoring………………………………..…35 Merrimack River Water Body Selection…………………35 3.2.2 Selection of Water Bodies for Study……………………….37 3.2.3 Risk Assessment Procedure………………………………..39 3.2.4 Selection of Exposure Parameters…………………………41 Exposure Point Concentrations………………………….41 Ingestion Rate……………………………………………42 Calculation of Ingestion Rates…………………………...44 Exposure Frequency……………………………………..45 Exposure Duration……………………………………….45 Relative Absorption Factor………………………………46 Body Weight……………………………………………...46 Averaging Period………………………………………...46 3.2.5 Risk Characterization……………………………………...46 Hazard Index (HI)………………………………………..47 Determining Reduction in Risk…………………………..47 4.0 RESULTS…………………………………………………………...49 4.1 Results of Risk Calculations…………………………………49 Exposure Calculation…………………………………….49 Exposure Point Concentration…………………………...49 4.2 Summary Risk Tables for Merrimack River Watershed……..50 4.3 Summary of Percent Change in Risk from Year to Year…….51 Chadwicks Pond………………………………………….52 Haggetts Pond……………………………………………53 Johnsons Pond…………………………………………...54 Lake Attitash……………………………………………..55 Lake Cochichewick………………………………………56 Pomps Pond……………………………………………...57 Stevens Pond……………………………………………..58 4.4 Summary of Percent Change in Risk from Baseline HI(1999) to Later Years.....………………………………………………...59 5.0 DISCUSSION……………………………………………..………...61 5.1 Varying Parameters and Risk Classification……………...….61 5.1.1 U.S. EPA Reference Dose (RfD) Versus ATSDR Minimal Risk Level( MRL)….……………………..……62 5.1.2 Calculated Risk Using Multipliers………………....63 5.2 Tipping Point and Massachusetts Department of Public Health Risk Management Approach……………………………………..64 5.2.1 Current Fish Consumption Advisories…………….64 Chadwicks Pond………………………………………….66 Haggetts Pond…………………………………………....66 Johnsons Pond…………………………………………...67 Lake Attitash……………………………………………..68 Lake Cochichewick………………………………………69 v Pomps Pond……………………………………………...69 Stevens Pond……………………………………………..70 5.3 Observations of Year-to-Year Trends and Effects of Sample Size and Average Fish Weight………..………………………….72 Chadwicks Pond………………………………………….72 Haggetts Pond……………………………………………72 Johnsons Pond…………………………………………...76 Lake Attitash……………………………………………..77 Lake Cochichewick………………………………………79 Pomps Pond……………………………………………...80 Stevens Pond……………………………………………..82 5.4 Discussion of Percent Changes of Baseline HI(1999) to Later Years Sampled…………………………………………………………..84 5.4.1 Acceptance of Alternative Hypothesis……………..85 5.5 Risk Levels from Consumption of Different Species………..85 5.6 Communicating Health Risk in Risk Management………….86 5.7 Regulation and Risk Interpretation…………………………..89 5.8 Future Research……………………………………………...90 5.9 Uncertainty Analysis…………………………………………92 Small Data Sets…………………………………………..92 Temporal Issues………………………………………….93 Exposure Uncertainties…………………………………..93 Dietary Preferences……………………………………...93 Intake…………………………………………………….93 6.0 CONCLUSIONS AND RECOMMENDATIONS………………………...95 6.1 Conclusions…………………………………………………..95 6.2 Recommendations……………………………………………97 6.3 Epilogue…………………………………………………….100 REFERENCES……………………………………………………..…………101 APPENDICES Appendix A Maps of the Merrimack River Watershed Appendix B HI Summary Tables Appendix C Species-Specific EPCs per Year Appendix D Full Risk Calculations vi LIST OF TABLES Table 3-1 Merrimack River Water Bodies Data Table 3-2 Dose-Response Values Table 3-3 Exposure Profile Summary Table 3-4 Species Specific Exposure Point Concentrations (mg/kg ww) Table 3-5 Fish Ingestion Rate Summary for Several Surveys Table 3-6 Summary of Exposure (Ingestion) Frequency Table 4-1 Summary of Exposure Calculation Inputs Table 4-2 Summary of Percent Changes in Risk from Year to Year Table 4-3 Summary of Percent Change from Baseline HI(1999) Table 5-1 Multipliers for Child 7-16, Adult, and Woman of Childbearing Age In Comparison to Child 2-6 Table 5-2 Merrimack River Watershed Freshwater Fish Consumption Advisories Table 5-3 Exposure Scenario, in Meals per Year, with Risks (HI) Greater than 1 for Child 2-6 at Chadwicks Pond Table 5-4 Exposure Scenario, in Meals per Year, with Risks (HI) Greater than 1 for Child 2-6 at Haggetts Pond Table 5-5 Exposure Scenario, in Meals per Year, with Risks (HI) Greater than 1 for Child 2-6 at Johnsons Pond Table 5-6 Exposure Scenario, in Meals per Year, with Risks (HI) Greater than 1 for Child 2-6 at Lake Attitash Table 5-7 Exposure Scenario, in Meals per Year, with Risks (HI) Greater than 1 for Child 2-6 at Lake Cochichewick Table 5-8 Exposure Scenario, in Meals per Year, with Risks (HI) Greater than 1 for Child 2-6 at Pomps Pond Table 5-9 Exposure Scenario, in Meals per Year, with Risks (HI) Greater than 1 for Child 2-6 at Stevens