Environmental toxicology
Environmental toxicology is a multidisciplinary field of science concerned with the study of the harmful effects of various chemical, biological and physical agents on living organisms. Ecotoxicology is a subdiscipline of environmental toxicology concerned with studying the harmful effects of toxicants at the population and ecosystem levels.
Rachel Carson is considered the mother of environmental toxicology, as she made it a distinct field within toxicology in 1962 with the publication of her book Silent Spring, which covered the effects of uncontrolled pesticide use. Carson's book was based extensively on a series of reports by Lucille Farrier Stickel on the ecological effects of the pesticide DDT.
Organisms can be exposed to various kinds of toxicants at any life cycle stage, some of which are more sensitive than others. Toxicity can also vary with the organism's placement within its food web. Bioaccumulation occurs when an organism stores toxicants in fatty tissues, which may eventually establish a trophic cascade and the biomagnification of specific toxicants. Biodegradation releases carbon dioxide and water as by-products into the environment. This process is typically limited in areas affected by environmental toxicants.
Harmful effects of such chemical and biological agents as toxicants from pollutants, insecticides, pesticides, and fertilizers can affect an organism and its community by reducing its species diversity and abundance. Such changes in population dynamics affect the ecosystem by reducing its productivity and stability.
On individual level, these toxins can cause severe health effects such as allergic reaction, stomachache and diarrhea, and death.
Although legislation implemented since the early 1970s had intended to minimize harmful effects of environmental toxicants upon all species, McCarty has warned that "longstanding limitations in the implementation of the simple conceptual model that is the basis of current aquatic toxicity testing protocols" may lead to an impending environmental toxicology "dark age".
Governing policies on environmental toxicity
U.S. policies
To protect the environment, the National Environmental Policy Act was written. The main point that NEPA brings to light is that it "assures that all branches of government give proper consideration to the environment prior to undertaking any major federal actions that significantly affect the environment." This law was passed in 1970 and also founded the Council on Environmental Quality. The importance of CEQ was that it helped further push policy areas.CEQ created environmental programs including the Federal Water Pollution Control Act, Toxic Substance Control Act, Resources Conservation and Recovery Act. CEQ was essential in creating the foundation for most of the "current environmental legislation except for Superfund and asbestos control legislation."
Some initial impacts of NEPA pertain to the interpretation within Courts. Not only did Courts interpret NEPA to expand over direct environmental impacts from any projects, specifically federal, but also indirect actions from federal projects.
Toxic Substance Control Act
TSCA, also known as the Toxic Substance Control Act, is a federal law that regulates industrial chemicals that have the potential to be harmful to humans and the environment. TSCA specifically targets "the manufacture, importation, storage, use, disposal, and degradation of chemicals in commercial use." The EPA allows the following to be done: "1. Pre-manufacture testing of chemicals to determine health or environmental risk 2. Review of chemicals for significant risk prior to the start of commercial production 3. Restriction or prohibition on the production or disposal of certain chemicals 4. Import and export control of chemicals prior to their entering or leaving the USA."The Clean Air Act
The Clean Air Act was aided by the signing of the 1990 amendments. These amendments protected reducing acid, the ozone layer, improving air quality and toxic pollutants. The Clean Air Act was actually revised and with, support from President George H.W Bush, it was signed in. The biggest major threats that this act targets are: urban air pollution, toxic air emissions, stratospheric ozone, acid rain etc. Apart from targeting these specific areas, it also established a national operating that "permits program to make the law more workable, and strengthened enforcement to help ensure better compliance with the Act."Regulations and enforcement actions on polychlorinated biphenyls
As mentioned above, though the United States did ban the use of polychlorinated biphenyls, there is the possibility that they are present in products made before the PCB ban in 1979. The Environmental Protection Agency released its ban on PCBs on April 19, 1979. According to the EPA, "Although PCBs are no longer being produced in this country, we will now bring under control the vast majority of PCBs still in use," said EPA Administrator Douglas M. Castle. "This will help prevent further contamination of our air, water and food supplies from a toxic and very persistent man-made chemical."PCBs has been tested on laboratory animals and have caused cancer and birth defects. PCB is suspected of having certain effects on liver and skin of humans. They are also suspected of causing cancer as well. EPA "estimates that 150 million pounds of PCBs are dispersed throughout the environment, including air and water supplies; an additional 290 million pounds are located in landfills in this country." Again, even though they have been banned, there is still a large amount of PCBs are circulating within the environment and are possibly causing effects on the skin and liver of humans.
There were some cases in which people or companies that disposed of PCBs incorrectly. Up until now, there have been four cases in which EPA had to take legal actions against people/companies for their methods of disposal. The two cases involving the companies, were fined $28,600 for improper disposal. It is unknown what fined was charged against the three people for "illegally dumping PCBs along 210 miles of roadway in North Carolina."
Though PCBs were banned, there are some exceptions where they are being used. The area in which it has been completely prohibited is "the manufacture, processing, distribution in commerce, and "non-enclosed" uses of PCBs unless specifically authorized or exempted by EPA. "Totally enclosed" uses will be allowed to continue for the life of the equipment." In terms of electrical equipment containing PCBs is allowed under specific controlled conditions. Out of the 750 million pounds of PCBs, electrical equipment represents 578 million pounds. Any new manufacture of PCB is prohibited.
PCBs
PCBs are organic pollutants that are still present in our environment today, despite being banned in many countries, including the United States and Canada. Due to the persistent nature of PCBs in aquatic ecosystems, many aquatic species contain high levels of this chemical. For example, wild salmon in the Baltic Sea have been shown to have significantly higher PCB levels than farmed salmon as the wild fish live in a heavily contaminated environment.PCBs pertains to a group of human-produced "organic chemicals known as Chlorinated hydrocarbons" The chemical and physical properties of a PCS determine the quantity and location chlorine and unlike other chemicals, they have no form of identification. The range of toxicity is not consistent and because PCBs have certain properties they have been used in a colossal amount of commercial and industrial practices. Some of those include, "Electrical, heat transfer and hydraulic equipment, plasticizers in paints, plastics and rubber products and pigments, dyes and carbonless copy paper" to name a few.
Heavy metals
Metals like cadmium, mercury, and lead have minimal roles in living organisms if any, so the accumulation of these, even if a little, can lead to health issues.For example, because humans consume fish, it is important to monitor fishes for such trace metals. It has been known for a long time that these trace metals get passed up the food web because of their lack of biodegradability or capability to break down. Such build-up can lead to liver damage and cardiovascular diseases in people. It is also important to monitor fishes not just for public health, but also to assess the health of coastal ecosystems.
For instance, it has been shown that fish exposed to higher cadmium levels and grow at a slower rate than fish exposed to lower levels or none. Moreover, cadmium can potentially alter the productivity and mating behaviours of these fish.
Heavy metals can also alter the genetic makeup in aquatic organisms. In Canada, a study examined genetic diversity in wild yellow perch along various heavy metal concentration gradients in lakes polluted by mining operations. Researchers wanted to determine what effect metal contamination had on evolutionary responses among populations of yellow perch. Along the gradient, genetic diversity over all loci was negatively correlated with liver cadmium contamination. Additionally, there was a negative correlation observed between copper contamination and genetic diversity. Some aquatic species have evolved heavy metal tolerances. In response to high heavy metal concentrations a Dipteran species, Chironomus riparius, of the midge family, Chironomidae, has evolved to become tolerant to cadmium toxicity in aquatic environments. Altered life histories, increased cadmium excretion, and sustained growth under cadmium exposure is evidence that shows that C. riparius exhibits genetically based heavy metal tolerance.
Additionally, a case study in China looked at the concentrations of Cu, Cr, Cd, and Pb in the edible parts of the fishes Pelteobagrus fluvidraco, the banded catfish, and Cyprinus carpio, the common carp living in Taihu Lake. These metals were actively being released from sources such as industrial waste stemming from agriculture and mining and then going into coastal ecosystems and becoming stored in the local fish, especially their organs. This was especially alarming because too much copper consumption can lead to diarrhea and nausea in humans and liver damage in fish. Additionally, too much lead can lead to defects in learning, behavior, metabolism, and growth in some vertebrates, including humans. Much of these heavy metals were found in the two fish species' liver, kidney, and gills, however, their concentrations were fortunately found to be below the threshold amount for human consumption made by the Chinese Food Health Criterion. Overall, the study showed that the remediation efforts here did in fact reduce the amount of heavy metals built up in the fish.
Generally speaking, the specific rate of build-up of metals in fish depends on the metal, the fish species, the aquatic environment, the time of year, and fishes' organs. For example, metals are more commonly known to be found the most in carnivorous species with omnivorous species following behind. In this case, perhaps due to the properties of the water differing at different parts of the year, there were more heavy metals spotted in the two fish species in the summer compared to the winter. Overall, it is relatively understood that the amount of metals in the liver and kidney of a fish represents the amount that has been actively stored in their bodies whereas the amount of metals in the gills represents the amount that has been accumulated from the surrounding water. This is why the gills are thought to be better bioindicators of metal pollution.