FISH TISSUE CONTAMINATION IN THE STATE OF MAINE
Regional Environmental Monitoring and Assessment Program (REMAP)
David Courtemanch, Barry Mower, Linda Bacon, and Jeanne DiFranco
Maine Department of Environmental Protection
This project was funded by the U.S. Environmental Protection Agency, and was undertaken in cooperation with the Maine Department of Inland Fisheries and Wildlife, the Maine Department of Human Services, and the University of Maine at Orono.
BACKGROUND
Since the late 1970's, high levels of mercury and other contaminants have occasionally been found in Maine fish, including those caught in remote, pristine lakes. Recent studies to investigate the low reproductive rate of Maine's bald eagle populations revealed high concentrations of mercury and PCB's in nesting eaglets.
Based on these findings, scientists became concerned about the potential risks to Maine's fish and wildlife resources, and to human health. In 1993, the Maine Department of Environmental Protection (DEP) initiated a study to measure levels of contamination in fish populations in the State's lakes and ponds.
EXPERIMENTAL DESIGN
From a population of 1800 candidate lakes, 150 target lakes were randomly selected using USEPA's statistical design program (EMAP ). This method is based on probability sampling.
During the summers of 1993 and 1994, fish, water, and sediment samples were collected form 127 of the target lakes. Additional water quality data were recorded in the field. The remaining target lakes were not samples due to constraints such as accessibility and availability of desired fish species.
OBJECTIVES
The purpose of this study is to estimate concentrations of mercury, cadmium, lead, PCB's, and selected pesticides in fish populations of Maine lakes, and to determine risks to human and wildlife consumers. Other goals are to estimate the number of lakes impacted, and to identify sources and patterns of contamination.
Factors which may affect a lake's sensitivity to contamination, such as geography, bedrock geology, water and sediment chemistry, hydrology, trophic state, and air flow patterns, will be examined. It may then be possible to develop preventive actions and management techniques. The project will also provide valuable baseline data for future research.
FISH COLLECTION
Fish species were targeted for collection based on trophic level considerations. The objective was to collect a top predator species (10 individuals) and an omnivore species (5 individuals) from each lake. A hierarchical order of preference was developed according to species distribution and desirability as a game fish. Target fish lengths were also developed in an effort to obtain fish of comparable ages.
Fish were collected by angling, gill nets, trap nets, dip nets, or beach seines. The length and weight of each individual was recorded, and any anomalies, such as tumors, lesions, and parasites were noted. Fish were wrapped in aluminum foil, labeled and frozen immediately upon returning from the field.
FISH TISSUE ANALYSIS
To determine potential risks to humans as well as wildlife, both fillets and whole fish were analyzed for contaminants. Fish from each lake were divided into three samples: whole fish predators, whole fish omnivores, and predator fillets. Fillets were analyzed from predators only, since humans prefer to consume these species.
The fish or fillets from each sample were ground, combined, and homogenized. A subsample of the resulting composite tissue was then extracted for analysis. Fillets were analyzed for mercury only, while whole fish analyses included mercury, cadmium, lead, PCB's, and pesticides.
WATER QUALITY
Water quality was sampled at the deep hole of each lake. The latitude and longitude of sampling stations were recorded using a Trimble Pathfinder Global Positioning System (GPS). A YSI 6000 Multiprobe with an Omnidata PC-286LX was used to measure and record profiles for temperature, dissolved oxygen, pH, and specific conductance. Secchi disk transparency was also measured.
Grab samples were taken at various depths for total alkalinity, dissolved organic carbon, anions, cations, true color, pH, acid neutralizing capacity, and total phosphorus analyses. An epilimnetic core sample for total phosphorus was collected with Tygon tubing.
SEDIMENT
A sediment sample was collected with an Ekman dredge from the deep hole of each study lake. The top 2 centimeters of sediment were transferred with an acid-washed plastic spoon equally into 3 Nalgene bottles. Care was taken to avoid contact with the sides of the dredge. Sediment appearance, depth and the number of dredges were recorded.
Sediment samples were frozen immediately upon return from the field, and later analyzed for mercury, cadmium, lead, total organic carbon, grain size, and percent moisture/solids.
PRELIMINARY FINDINGS
Based on preliminary data evaluation, fish composite mercury levels of 0.43 ppm or higher were found in 65% of the lakes sampled. This is the level of concern for human consumption established by the Maine Department of Human Services. Fish composites from 9% of the study lakes also exceeded the Federal Food and Drug Administration action level of 1.0 ppm.
As a result of these findings, the State of Maine issued a mercury health advisory in May 1994. The advisory may be revised pending further analysis of the mercury results.
