Bioaccumulation refers to the gradual increase of toxic chemicals in the body tissues of living organisms over time. It occurs because the chemicals cannot be broken down by the organism (that is, it cannot be metabolized). Bioaccumulation may not be of a concern if the compounds in question are not harmful. However, harmful compounds such as lead and mercury can accumulate in the body tissues of living organisms. The source of pollutants that bioaccumulate in the body include pesticides, industrial chemicals, and by-products. Rainwater can transport residues of pesticides used in the farms in the creeks and eventually find their way into rivers, streams, estuaries, and oceans, among other water bodies. Automobile emissions and industrial smokestacks are among the leading source of toxic pollutants found in the environment. They return to the ground when it rains, and they find their way into water bodies in different ecosystems. Deliberate discharge of pollutants in the environment is also another source of contaminants.
Bioaccumulation And Biomagnification
Bioaccumulation is the gradual buildup of chemical toxins in the body tissues of an organism. It occurs when the uptake of chemical toxins by the organism is faster than the rate it is lost through excretion or catabolism. It implies that if the biological half-life of the chemical toxins is greater, then the risk of poisoning will be higher even if the levels of toxins in the environment are low.
On the other hand, biomagnification, also known as bioamplification, refers to the concentration of chemical toxins that increases progressively along the food chain. Bioaccumulation and biomagnification are processes that take place in tandem. Biomagnification traces the movement of toxic pollutants through different trophic levels within an ecosystem. In a food chain, energy is typically transferred from one lower trophic level to another higher level, as one organism consumes another. However, it is not energy alone that is transferred in the food chain, but also pollutants ingested by organisms.
Bioaccumulation And Biomagnification In The Food Chain
Bioaccumulation typically occurs at the bottom of the food chain, particularly among the primary producers, for instance, the phytoplankton. These microscopic organisms absorb Persistent Organic Pollutants (POPs) directly from their ecosystems (oceans) that accumulate in their bodies over a period of time. The pollutants build up in their body tissues because they absorb them from water at a rate that is higher than the rate they can eliminate. Biomagnification takes place when larger organisms such as zooplankton consume phytoplankton, which is already contaminated and therefore absorbs the POPs that accumulate in their own body tissues at a higher concentration. As zooplankton consumes more of contaminated phytoplanktons, the more pollutants will accumulate in their bodies. The POPs are transferred from producers to primary consumers, secondary consumers, and finally to the top of the food chain. Biomagnification continues at each trophic level to the apex of the food chain. The POPs become more concentrated on each subsequent trophic level, and therefore the apex predators in the oceans are at high risk of fatal levels of POPs.
Persistent Organic Pollutants (POPs)
According to the World Health Organization, persistent organic pollutants (POPs) refer to chemical pollutants of global concern. These toxic pollutants have the potential to persist in the environment and have a long-range transport, as well as the ability to bioaccumulate and biomagnify in different ecosystems. As a result, they have a significant adverse impact on the environment and human health and other animals. People are exposed to these pollutants in different ways, which include food that we consume, the air we breathe indoors, outdoors, and workplaces. Besides, several products used every day in our lives may contain POPs that have been added for the purposes of improving the quality of the products, for instance, surfactants and flame retardants. Therefore, POPs are found almost everywhere in measurable concentrations around the world. Some of the sources of POPs include organochlorine pesticides like Dichlorodiphenyltrichloroethane (DDT), Industrial chemicals such as polychlorinated biphenyls (PCB), as well as by-products of other industrial processes such as polychlorinated dibenzo-p-dioxins (PCDD), and dibenzofurans (PCDF), popularly known as dioxins among many others.
Minamata disease refers to the poisoning of methylmercury (MeHg) that affects people who have ingested shellfish or fish contaminated by methylmercury. Methylmercury finds its way from industrial waste to the oceans. Minamata disease was first discovered in May 1956 in Minamata City, Kumamoto prefecture in the southern part of the Japanese island of Kyushu. Chisso Corporation was responsible for discharging its industrial waste on a massive scale into Minamata bay between 1932 and 1968. At the time, it was not clear as to the cause of the disease. The marine products from the bay exhibited a high level of Mercury (Hg) contamination of between 5.6 ppm and 35.7 ppm. Similarly, the patients had high Hg levels in their hair, and the residents of the Shiranui coastline also had high concentrations of mercury, some with as high as 705 ppm.
The highly toxic methylmercury bioaccumulate in fish and shellfish found in Shiranui and Minamata. The poisoning affected humans, pigs, cats, dogs, and birds, among other animals. Some of the symptoms of Minamata disease include ataxia, sensory disturbance, dysarthria, auditory, and visual impairment. Fetuses were also affected by mercury poisoning through mothers who ingested contaminants from marine products. The disease was named congenital Minamata disease. It was observed that the number of grave incidences with acute Minamata disease was decreasing during the initial stages; however, the number of cases with chronic Minamata disease showing symptoms over a long time was on the increase. Records indicate that a total of 2,265 people affected by Minamata disease had been officially identified as of March 2001, out of which 1,784 had died.
Global issues On POPs
POPs are potentially harmful to human health, and they can adversely affect the environment. These harmful chemicals can be transported by water or wind over long distances causing harm to people and wildlife in different countries from where they were disposed of or generated. POPs can persist in the environment for long and therefore bioaccumulating and biomagnifying along the food chain. The US, with other 90 countries, including the EU, signed a groundbreaking UN treaty in Sweden in 2001. The treaty is known as the Stockholm Convention. The countries agreed to eliminate or reduce the use, production, and release of 12 main POPs of global concern. Since then, several other POPs of global concern have been added.
Some Of The POPs On Stockholm Convention
Most of the POPs covered in the Stockholm convention are no longer produced in most of the developed countries. However, different habitats in most of these countries may be at risk because of these toxic chemicals which have persisted in the environment originating from unintentionally produced POPs originating within these countries or from other regions.
DDT was commonly used during WWII to control insects that spread typhus and malaria, among other diseases. After the war, it was used to control diseases and insects among agricultural crops, particularly cotton. DDT is still used in different countries to control mosquitoes that cause malaria. DDT has stability and persistence, and up to 50% could remain in the soil for as long as 15 years following application. Its residues can be found everywhere because of its widespread use in the past. The DDT residuals have been found in the Arctic. In 1970, Sweden, Norway, and Hungary banned the use of DDT, and in 1972, it was banned in the US, Canada, and Germany. The total ban in the EC was in 1983, and the UK banned the use of DDT in 1984. Australia banned the use of DDT in 1987.
Other POPs On Stockholm Convention
Other than DDT, the other POPs include pesticides such as endrin, dieldrin, chlordane, aldrin, toxaphene, mirex, hexachlorobenzene, and heptachlor. In the list are industrial products such as polychlorinated biphenyls (PCBs) and hexachlorobenzene. Different by-products are also listed, and they include polychlorinated dibenzo-p-dioxins, hexachlorobenzene, and polychlorinated dibenzofurans, and PCBs. Other than the original 12 POPs listed, several others have been added since 2001. By 2017, sixteen new POPs had been added.
Effects Of POPs
POPs are toxic chemicals that biomagnify along the food chain, and they also bioaccumulate in the tissues of organisms. As a result, the highest concentrations of POPs are found in the apex predators, or organisms are the top of the food chain. This implies that POPs in the environment would eventually be found in the human body. It has been established that POPS affect the immune, reproductive, and endocrine systems. They are linked to causing a myriad of neurobehavioral impairments, genotoxicity, thyroid problems, diabetes, birth defects, and cancer, among others.
According to longitudinal studies, infants whose mothers ingested substantial amounts of contaminated fish from Lake Michigan indicated that they had shorter attention span, small head circumference, and lower birth weight compared to infants whose mothers did not consume the contaminated fish. Over the years, there has been significant deteriorating health of marine mammals, and most of the resurgent and emerging diseases are associated with dysfunction of the immune system, which suggests a wide environmental distress syndrome. The metabolic imbalance is one attribute associated with marine mammals, and they are considered the most vulnerable regarding long-term toxicity of human-made chemicals like organochlorides. Dolphins and Whales (Cetaceans) have a poor ability to get rid of organic pollutants because they do not have isozymes needed to detoxify pollutants such as PCBs and DDT.