Contaminants in the Environment

There are two issues to consider about environmental contaminants: fate - what happens to the contaminant when released to the environment, and effect - what kind of damage is done.

Fate Some contaminants are short-lived in the environment and consequently affect only the immediate areas for a short time, while others persist for decades. Long-lived chemical contaminants may remain at the area of release or may be transported to other locations. For example, chemicals dumped onto the ground may adsorb to soil particles and persist there for decades. Other chemicals leach into the groundwater or adjacent streams, rivers, and lakes and are transported away from the site of disposal. The type of soil also affects fate of chemicals. Some soils, like sand, are more permeable and allow water to readily pass through and carry contaminants into the groundwater. Other soils, such as clay, are less permeable and allow liquids to filter through slowly enough that surface runoff will will carry most of the contaminants into nearby water bodies. Some chemicals dumped onto land will adsorb to the organic fraction of soil; some chemicals dumped into water bodies will adsorb onto the bottom sediments and persist for decades. Chemical contaminants emitted into air may be carried up to hundreds or thousands of miles by prevailing winds.

Effect The effect of any chemical contaminant depends on its toxicity and the quantity released. At high concentrations, contaminants dumped into water bodies can cause acute toxicity (death) to aquatic organisms, whereas, at lower concentrations they may cause chronic effects, such as decreased growth rate, reduced offspring, nervous system disorders, or may accumulate in the tissues. Edible species may accumulate high enough concentrations of certain chemicals that they pose a human health threat; for example, fish and shellfish from New Bedford Harbor accumulate PCBs to make them unsafe to eat. Since some species of plants and animals are more sensitive than others, pollutants may alter the species composition by affecting the more sensitive species, while the more tolerant ones survive.

Contaminants in the Acushnet River watershed The groups of contaminants mentioned on this web page all pose some sort of problem when released into the environment. The fate and effect of contaminants released in the Acushnet River watershed can be described in general terms (see below); the particular effect of a contaminant depends on the individual chemical or mix of chemicals, the amount released, and the physical characteristics of the disposal site.

Metals Various metals that are commonly used in industrial processes are toxic and insoluble. That means that they adsorb to sediments, can be accumulated by organisms, and persist in the environment. Sediments in New Bedford Harbor contain high concentrations of metals, particularly copper, chromium, zinc, and lead.

Cyanide Cyanide is highly toxic and persists in the environment. It was used by several industries in the 1800s, but is now regulated. Industries in New Bedford that may have released cyanide as a pollutant were coal-gas production and metal plating.

Petroleum hydrocarbons Petroleum hydrocarbons are comprised of hundreds of organic compounds derived from petroleum. Toxicity and persistence depend on the particular fraction of petroleum. Some petroleum fractions are volatile (evaporate easily) and do not persist in the environment. Although volatile compounds are toxic, they usually are not harmful to organisms because they do not stay around long enough. The less-volatile fractions are less reactive, persist longer in the environment, and are toxic. Oils and grease are general terms for some petroleum hydrocarbons.

Phenols Phenols, a particular group of organic chemicals, vary in toxicity and tend to be less persistent in the environment. Industries in New Bedford that may have used phenols were metal working industries, petroleum refining, and coal-gas production.

Solvents Solvents are chemicals distinguished by their industrial use rather than their chemical structure. They are usually organic chemicals. Solvents vary in toxicity and persistence in the environment. They were used in many industries: dying, metalworking, printing, tanning, and manufacturng glass, electric and electronic parts, plastics, paint and varnish, and rubber products.

Acids Acids can cause acute effects in the immediate disposal area, but they do not persist in the environment because they are quickly buffered. Industries in New Bedford that likely used acids were metal-working and metal plating, printing, petroleum refining, tanning, and manufacturing rubber products.

Lye and caustic cleaning agents Lye and caustic cleaning agents are highly toxic. They can cause acute effects where they are dumped, they are very reactive and do not persist in the environment. Lye was used in tanning and soap making.

Biological wastes Biological wastes can cause acute, short-term effects when disposed in water. Biological wastes contain organic matter, which consumes dissolved oxygen (DO) as it decomposes. The amount of DO in waters can be lowered so much that resident plants and animals can not survive. Industries in New Bedford that may have released biological wastes were tanning operations (hides and animal waste), fish processing plants (fish wastes), processing whale oil (although most of the initial processing of whale oil was done aboard the whaleships), and manufacture of rubber products.

Contaminants in the Environment

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