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CASCO BAY PLAN
 
 
 

When it rains or snows, the soil particles and organic matter in runoff water pick up oils, metals, pesticides, and other contaminants. The contaminants adhere to the soil or organic matter rather than mixing readily into water. Once in the bay, organic contaminants may float to the surface to avoid water, forming a sea-surface microlayer. Other contaminants adhere to sediments and particles of organic detritus. Initially, sediment and particles settle to the sea bottom near where they enter marine waters, though over time they may get dispersed by tides, currents, storms, or dredging. Water that lies over contaminated sediments may even test as clean because the toxics tend not to be water-soluble. 

ATMOSPHERIC DEPOSITION SOURCES OF TOXIC POLLUTION

Atmospheric deposition is a natural process by which pollutants are transferred from air to soil, surface water, sediment, and groundwater and potentially to living organisms.  Wet and dry deposition processes (e.g., rain out, wash out, impaction, adsorption and absorption) remove particulate and gaseous pollutants from the atmosphere and deposit them on the surface of water bodies, vegetation, buildings and structures, and soil. 

The current role of atmopsheric deposition, as it relates to nitrogen, mercury and fine partulcate matter pollution in Casco Bay, needed to be better understood and quantified.  In response to this need, the Casco Bay Estuary Partnership (formerly Casco Bay Estuary Project) Air Deposition Team started collecting samples at a site in Freeport.   Sonoma Technology Inc. was hired to validate and analyze the data resulting in the July 3, 2003 report "Deposition of Air Pollutants to Casco Bay."

Follow this link for a slideshow presentation of the results from the Casco Bay Estuary Project air deposition monitoring in Freeport.  Please be aware that this slideshow file is 4.5 MB. It is best viewed in Internet Explorer (it will show in Netscape, however, it doesn't have the option to run automatically. 

The Casco Bay Air Deposition Study Team also prepared a document that provides a simple method for estimating the annual rate of direct atmospheric deposition of pollutants to an estuary when little or no local monitoring data is available.  "Estimating Estuarine Pollutant Loading From Atmospheric Deposition Using Casco Bay, Maine as a Case Study."  (17 MB pdf)  The paper compares the estimates developed for rate of deposition of nitrogen, mercury and PAHs to the Freeport field monitoring results.  The estimation approach is a useful starting point for understanding the sources of pollutants entering water bodies that cannot be accounted for through run-off or point source discharges. 

The most common toxic pollutants in Casco Bay are Polyaromatic Hydrocarbons (PAHs), a class of organic compounds primarily found in fossil fuels such as oil or coal. Most PAHs found in the sediments of the bay come from combustion sources (i.e., car and truck exhausts, and industrial and residential chimneys). PAHs enter the bay through combined sewer overflows and storm drains (particularly those that drain roads and parking lots), licensed discharges, old industrial sites or dumps, spills, deposition of atmospheric pollution from urban sources in and upwind of Maine, and highly developed residential and industrial areas in the bay watershed. Hydrocarbon pollution, another source of PAHs, is aggravated by the roughly 70 reported spills each year in Maine coastal waters.

For more information specific to the PAH analysis of the Freeport monitoring data read Dr. Dan Golomb's research paper."Atmospheric deposition of polycyclic aromatic hydrocarbons near New England Coastal Waters." 

Metals in Casco Bay are concentrated in and around Portland Harbor. Sources are numerous, including vehicle emissions, licensed discharges, air deposition, and historic industrial sites. Evidence of these early industries remains in the bay. At the site of a former coal gas works plant, which operated in Portland for almost a century, coal tar can still be seen oozing into the Fore River estuary. 

Ecologic Effects

• Bottom-Dwelling Animals: While thorough studies of toxic impacts on bottom-dwelling life in Casco Bay have not been completed, there is some evidence of damage. Animals that would be expected to occur in the flats of Back Cove are missing, potentially due to such factors as oil-related contaminants, heavy metals, combined sewer overflow discharges, sedimentary disturbances, or a combination of factors. Benthic life in the inner Fore River has been dramatically impaired. 
• Fisheries: Sediment contamination can have serious ramifications for fisheries and marine life in Casco Bay. Fish and crustaceans can absorb toxics directly by exposure to contaminants in the water, and indirectly by eating contaminated food - particularly bottom-dwelling organisms that live and feed among the "modern mud" sediments on the bay's bottom. Blue mussels sampled in the outer Fore River had elevated levels of lead in their tissues, while those in the Presumpscot River had elevated levels of mercury. These findings confirm that mussels are accumulating metals, but do not indicate what harm is being done. Mussels are used nationally as an indicator species of toxic pollution. 
• Wildlife: Mammals and birds that feed on benthic organisms or fish may absorb concentrated amounts of contaminants. Some of the tidal mudflats that represent the most important feeding areas for shorebirds, waterfowl, and wading birds - the Fore River, Back Cove, and Presumpscot River - also have the highest concentration of contaminated sediments in the bay. 
• Human Health: Various toxic pollutants (e.g., PCBs, DDT, some PAHs, and dioxin) concentrate in the liver, fat, and tissue of animals and can cause significant human health impacts. Bioaccumulative toxic chemicals can cause cancer, adverse reproductive effects, birth and developmental effects, organ damage, and deleterious impacts on the nervous, immune, and endocrine systems. With the exception of testing for dioxin in lobsters and clams, and the testing of toxics in lobster and mussel tissue, there has been no risk assessment of potential health hazards from eating seafood in Casco Bay. 

• industrial and municipal cooperation with discharge permit limits and pre-treatment programs 
• reduction of combined sewer overflows 
• better oil-spill prevention 
• cleanup of some hazardous waste sites 
• implementation of best management practices in road construction, major development, farming, and forestry 
• elimination of leaded gasoline 
• increased awareness among citizens and boaters regarding safe disposal of toxic materials 
• discontinued use of shoreside dumps 

• To continue reducing levels of sediment contamination, more attention must now be focused on nonpoint sources such as runoff from roads and parking lots. If measures to reduce pollution are taken, the ecosystem will eventually cleanse itself. Contaminated sediments will become "biologically unavailable" as new sediments wash off the land and cover them, and chemical and degradative processes reduce their toxicity. And as cleaner sediments enter the bay, existing contaminants will be made less toxic through further dilution. 
• Plant native vegetation in and around your property to promote a variety of wildlife species (call CBEP for planting ideas, 780-4820). 
• Maintain vegetative buffer areas next to water. These buffers provide habitat and act as filters for stormwater and groundwater flow from upland development. 
• Cut down on your use of household hazardous waste such as solvents and cleaners and try the less toxic alternatives (CBEP has information on the alternatives). 
• Try not to use pesticides and herbicides on your lawn and garden. If you feel you must, use only in limited quantities and always provide vegetative buffers on your property, they help to take in the chemicals before they are further dispersed into the environment. 
• Keep a clean running car and other home equipment such as lawn mowers and boats. This will cut down on excess emissions such as oil and gas.