Function: Decomposition, mediation or storage of waste by biological, biochemical or biophysical processes

The estimation of speed of decomposition, mediation and storage processes is a challenge in ecosystem level while the conditions (temperature, moisture, acidity, nutrition and health of organisms) change. In laboratory conditions, the estimation is relatively easy for single compounds.

ORGANISMS

The main exposure and accumulation routes of the contaminants are via water, food and air. The most important factor affecting accumulation is fat –solubility of the compound: fat-soluble compounds accumulate to organisms more efficiently than water- soluble compounds. If a contaminant is stored in fat or other storage tissue, it won’t enter the metabolism of the organism and cause harm. However, if organism is using its energy storages, contaminants are released and may cause toxicological effects. Water- soluble contaminants are excreted out of the organism and rarely cause chronic effects, if exposure is non- recurring.

Fat- soluble contaminants bioaccumulate readily to the top predators of the ecosystems, because compounds stored in the fat of prey are transferred via feeding. Because of this most of the serious toxicological effects are observed in top predators.

One of the functions of metabolism is to transform potentially harmful compounds to less dangerous form. However, there are compounds, whose metabolites are more harmful than the parent compound or are the main cause of the toxic effects.  

A low exposure to contaminants may induce the activity of enzymes that metabolize contaminants, leading to improved resistance to the effects of pollutants. Populations locating on contaminated areas have usually higher resistance for pollutants than ones living in unpolluted environment. Fast reproducing organisms, e.g. microbes and invertebrates, may develop higher resistance in couple of generations by the effect of mutations and natural selection.

WATER

In water phase mediation and decomposition of contaminants is affected by compound’s fat- solubility, water’s acidity and temperature and amount of organic matter and light. Chemical reactions proceed faster in higher temperature and some compounds need exposure to sunlight to set chemical reactions in motion. Fat- soluble compounds bind readily to organic particles (e.g. humus) in water, which may reduce the exposure of organisms in humic waters. Hardness of the water also may have effects on accumulation and behavior of some contaminants (e.g. cadmium) in water and organisms.

SOIL

There are many factors that may affect the behavior of contaminants in terrestrial environment: characteristics of the compound, soil quality and temperature, acidity, amount of water and organic matter. Fat- soluble compounds bind readily to particles and organic matter (humus) in soil and are less likely to flow to ground water.  

The most important factors regulating decomposition of contaminants are temperature, acidity and soil water. Biodegradation of the compounds becomes more effective if soil organisms have optimal conditions. Acidity of the soil affects the ionization of the compound, and some ionic forms are more likely to enter chemical reactions.

Because chemicals have become common in soils, some strains of bacteria and fungi have developed ability to degrade organic pollutants like PAH- compounds. Using these strains in bioremediation of polluted soils has been under research for a long time by now. Usually contaminants need to be in soil water to be bioavailable to organisms, but there are some exceptions.