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Mercury concentrations in 58 rivers in Maine was measured to range from below detection up to 7.01 ng L(-1) and averaged 1.80 +/- 1.29 ng L(-1). The concentration gradient for mercury in rivers across the state was not uniform. Mercury strongly correlated with dissolved organic carbon (DOC) and aluminum, and less strongly with copper, lead, and zinc. Mercury exhibited significant differences in correlations with chemical variables and local geology when partitioned by flow state (high or low). Mercury concentrations were greatest in rivers flowing across either wacke-type bedrock at low metamorphic grade, or glacial-till deposits. Elevated concentrations of mercury formed a locus in northern Maine under both high and low-flow states while in southwestern Maine a locus formed only during high-flow states. These regional differences were statistically significant when compared by geographical location. We suggest that there is a bedrock source of mercury in northeastern Maine that is diluted during periods of high runoff. The elevated concentrations detected under high-flow states, as noted in southwestern Maine, may reflect mercury released from storage in association with DOC during periods of high runoff. The association of mercury with flow state indicates that watershed processes and local geology can modulate the concentration of mercury in rivers.

Since 1988, the State of Maine has monitored dioxin levels in the tissues of predatory and bottom feeding species of fish taken from the state's major water bodies, including five rivers which receive the effluent of bleached kraft paper mills. Data are also available on dioxin concentrations in the effluent of these mills. Monitoring results were analyzed using simple models to yield field bioaccumulation factors (BAFs) for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in Maine rivers. Three BAFs were computed for each fish species at each site to account for declining TCDD levels in mill effluents over time. Mean BAFs (across rivers) ranged from 11,500 to 24,600 for smallmouth bass fillets, from 17,900 to 28,300 for brown trout fillets, from 3000 to 7500 for white perch fillets, and from 78,500 to 106,000 for white sucker whole bodies. Field BAFs obtained in this analysis are similar to factors obtained in recent laboratory studies of TCDD accumulation in fish. Our results suggest that EPA's currently recommended BCF value of 5000 is probably too low. Instead, a value between 15,000 and 25,000 is considered a reasonable estimate of the BAF to use for regulatory purposes in the state of Maine.