• The Aggravation of Accumulation - Looks at the process of bioaccumulation of synthetic chemicals and the impact of this process on the food chain.

Bioaccumulation is the increase in the concentration of a chemical in a biological organism over time. Compounds accumulate in living things when they are absorbed and stored faster than they are metabolized or eliminated. Understanding bioaccumulation is important in protecting humans and other organisms from exposure to chemicals that may cause harm.

One of the first chemicals found to have harmful affects on the environment was DDT. By the 1950s, DDT was found to be causing the decline in bald eagle and other bird populations due to the thinning of eggshells. In 1962, the biologist Rachel Carson, wrote about the impacts of pesticides on wildlife and human health in her book, Silent Spring, a landmark for the environmental movement.

The following graphic illustrates a typical food chain:

Algae is eaten by the water flea eaten by a minnow eaten by a trout and finally consumed by an osprey.

Uptake occurs when an organism ingests a substance by breathing, swallowing, or absorbing it through the skin. Storage of a chemical in a body tissue or an organ. Bioconcentration is when there is a net accumulation of a chemical in an organism as a result of intake and elimination. Biomagnification is the increased accumulation in the concentration of a chemical as it moves up through the food chain.

Persistent Organic Pollutants (POPs) are synthetic chemicals that resist the normal processes of degradation. They are carbon-based chemical compounds that share four characteristics: high toxicity, persistence, fat soluble, and ability to evaporate for travelling long distances.

There are 12 top POPs (called "the Dirty Dozen" by environmental groups) targeted by an international community of governments, scientists and environmental groups for banning. They include: 8 pesticides (aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex, and toxaphene); 2 types of industrial chemicals (polychlorinated biphenyls or PCBs and hexachlorobenzene); and, 2 types of by-products of the manufacture, use, and/or combustion of chlorine and chlorine-containing materials (dioxins and furans).

Banning harmful chemicals works! In 1972, DDT was banned in the United States. Since then, the recovery of impacted species such as the Bald eagle and the Brown pelican have been well documented.

A pesticide is any chemical used to repel, kill or control fungi, animals, or plants. Pesticides are divided into different categories depending on the kinds of organisms they are used to control. Insecticides are used to control insect populations. Fungicides are used to kill fungal growths. Mice and rats are killed by rodenticides and unwanted plants are controlled with herbicides. Since many of the POPs have been banned in the US, the chemical industry has developed new pesticides called organophosphates and carbamates. These pesticides break down into harmless products in a few hours or days so they do not bioaccumulate. These new pesticides do have some side effects. They are not species specific and can kill beneficial species too. Since they do not last long in the environment more frequent applications must be performed which is more expensive. Also, these pesticides are much more toxic to humans and other vertebrates. Common types of organophosphates are malathion, parathion, and diazinon. Sevin, aldricarb and propoxur are examples of carbamates.

In order to eliminate the use of synthetic chemicals, some farmers are returning to the traditional methods of farming now called "organic farming." While they do experience smaller yields than farms that use synthetic chemicals, on an average, organic farms use only 40% of the energy used on conventional farms. This reduces costs and raises the profit margin.

Vocabulary:

uptake
storage
bioconcentration
biomagnification
POPs
pesticide
fungicides
rodenticides
herbicides
organophosphates
carbamates
organic
toxicity