Ecotoxicology is the study of toxic pollutants in ecosystems.(according to Encyclopedia Universalis)
- mechanisms of action of pollutants;
- prevention and monitoring of pollution;
- pollution management;
- anticipation of the effects of pollutants.
EXAMPLES OF ECOTOXICITY
Bioaccumulation – Minamata
The importance and dangers of bioaccumulation were revealed by the Minamata case.
Minamata is a small bay in Japan, communicating with the China Sea, where a fertilizer plant pours methylmercury during the 1950s. Throughout the food chain, methylmercury is concentrated in the tissues of plants and fish. While the concentration in the sea is very low, unmeasurable, that reached in fish is dangerous. First, cats and Minamata fishermen, who eat mainly bayfish, are intoxicated by mercury salts that cause acute encephalopathy with motor and sensory impairment. Many people died in the months that followed. Several thousand compensation cases have been filed.
Endocrine disruptors are also known as xenoestrogens. These are substances that modify endocrine function, especially sexual function and reproduction.
Although the term “endocrine disruptors” was not used at the time, their consequences were described, as early as 1962, by Rachel Carson in her book “Silent spring” where she blamed pesticides organochlorines cause of the disappearance of birds. This book is considered the starting point of the environmental movement.
Estrogenic effects have been detected with DDT and PCBs that cause feminization of gull embryos.
Many other pesticides have a similar effect. The same is true for certain drug residues which, when excreted in the urine, reach the natural environment via the treatment plants.
The cocktail effect is the combined effect of several pesticides.
Already, in 1962 R. Carson wrote, concerning two large classes of pesticides: “organic phosphates [organophosphorus], destructive cholinesterase, have a more pronounced effect on a subject already exposed to chlorinated hydrocarbons [organochlorines]; this is easily explained: the hydrocarbons have attacked the liver, the level of cholinesterase has already fallen below the normal, it is enough of a moderate action of the phosphates to trigger an acute poisoning. ” Unfortunately, more than 55 years later, the toxicity of pesticides is essentially tested in isolation and the cocktail effect is largely unknown.
Persistence of pollutants
Regardless of the intrinsic toxicity of a molecule and the possible bio concentration, another important factor influences the real danger: molecular stability. The more stable a molecule is, the longer it will persist in the environment and manifest its toxicity. To characterize the stability, the half-life time is used: the time at which 50% of the molecules are destroyed. The half-life is more than 10 years for DDT, a few years for dioxin and PCBs.
On the other hand, some molecules by degrading will form other substances, metabolites, whose toxicity may be higher than the starting molecule.
Food webThe food web is the representation of food exchanges between organisms in an ecosystem.
EutrophicationEutrophication is the process of enriching water with nutrients. The evolution is as follows:
- At first the water is cloudy which makes it unsuitable for swimming. It can also give off an unpleasant odor.
- Then the algae, some of which may be toxic, continue to grow. Swimming, which has become dangerous, is forbidden.
- Gradually the fish disappear.
This aging process is, in general, very slow and occurs at the geological time scale. Human activities can greatly accelerate it. This is a dysfunction of the eutrophication process called dystrophication.
BioconcentrationBioconcentration is the increase in the concentration of toxic products in an animal’s tissues relative to the environment in which they live (used for aquatic animals). The ratio between the two concentrations is the BCF (Bioconcentration factor).
BCF = C organism / C ambient water
The BCF can reach values of tens of thousands.
BiomagnificationBiomagnification is the concentration increase of a toxic product in organisms along the food chain. The total concentration increase is the product of the increase in each link.
BiodegradabilityBiodegradability is the ability of a molecule to be degraded by microorganisms (bacteria, algae, fungi …).
MetaboliteStable compound resulting from the degradation of an initial compound by metabolism.
Endocrine disruptorSubstances that modify endocrine function, especially sexual function and reproduction.
PECPEC is the predicted concentration in the environment due to dilution and different inputs. (PEC = Predicted Environmental Concentration).
PNECThe PNEC is the maximum concentration in the environment of a pollutant (PNEC = Predicted No Effect Concentration or concentration with no foreseeable effect on the environment). It is estimated from laboratory tests that determine a threshold above which the substance has an effect on the environment. PNECs are used for all toxic substances as well as drugs.
POPPersistent organic pollutants (POPs) are persistent, bioaccumulative, toxic and mobile substances.
POPs include dioxins, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs) and several pesticides.