Mercury, a neurotoxin that can lead to severe health and developmental problems, may be released into the atmosphere naturally through volcanic eruptions, mineral deposit exposures, and by ocean water evaporation, or industrially by waste incinerators, and coal burning and chlorine producing industries. Mercury can be carried via prevailing air currents where precipitation can absorb the atmospheric mercury and deposit it directly into water, or on land where it will be potentially transferred to water via runoff. Once mercury is introduced into the environment, it may be transformed to a more toxic form, methylmercury, which works its way through the food chain.

Our study involves an analysis of mercury in salt marsh sediment cores and surficial sediment grab samples on the Penobscott River, Maine, upstream, downstream, and adjacent to Holtrachem, a chlor-alkali plant located adjacent to the Penobscott River in Orrington, Maine, which uses mercury in the manufacturing process. Our results show a clear response of mercury input into the natural environment with respect to this point source. The highest concentration levels attained are from the initial salt marsh sediment core taken adjacent to Holtrachem in 1999. Later sampling in 2001, two years after plant shutdown, shows the second highest concentrations downstream and adjacent to Holtrachem. The lowest concentration values occur upstream from the Holtrachem plant. The grab samples taken adjacent to Holtrachem yield the highest concentrations of all the grab samples; by a factor of 10 compared to those collected upstream, and by a factor of 2-4 compared to those sampled downstream. These data reflect two possible sources of mercury input to the Penobscott River system. An atmospheric source as indicated by the upstream salt marsh sediment core, and a second Holtrachem point source shown by both the sediment grab samples and salt marsh sediment cores collected adjacent to and downstream from the Holtrachem plant in the Penobscott River.