User:Ecokelbells/Environmental toxicology

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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 (i.e. rainbow trout) 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 (copper), Cr (chromium), Cd (cadmium), and Pb (lead) 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. '''

Metals toxicity
The most known or common types of heavy metals include zinc, arsenic, copper, lead, nickel, chromium, aluminum, and cadmium. All of these types cause certain risks on human and environment health.

Aluminum

'''Aluminum is the most common natural metal in the Earth’s crust and is naturally cycled throughout the environment via processes like the weathering of rocks and volcano eruptions. Those natural processes release more aluminum into the freshwater environments than do humans, but anthropogenic impact has been causing values to rise above the recommended amount by the U.S. EPA and World Health Organization. Aluminum is used commonly in industrially-made items like paints, paper, household appliances, packaging, processing of food and water, and for health care items like antiperspirants and vaccine production.  Run-off from those industrial uses then bring the metal flowing into the environment. '''

'''Generally, too much exposure to aluminum affects motor and cognitive skills. In mammals, the metal has been shown to affect gene expression, DNA repair, and DNA binding. One study showed how the effects of aluminum include neurodegeneration and nerve cell death in mice. Another study has shown it to be related to human diseases associated with the nervous system such as Alzheimer’s and Parkinson’s disease and autism. '''

'''Exposure to contaminants can change the tissues of marine life like fish too. For example, its accumulation has been shown to cause neurodegeneration in cerebral regions of the brains such as those of O. mossambicus, otherwise known as Mozambique tilapia. Aluminum also decreases locomotive abilities of fishes since aluminum is thought to negatively impact with their oxygen supply.  Finally, the metal causes slow responses to arousal and other environmental stimuli, overall abnormal behavior, and changes with the neurotransmitters in their bodies such as adrenaline and dopamine. '''

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Mercury
Mercury, a shiny silver-white, can transform into a colorless and odorless gas when heated up. Mercury highly affects the marine environment and there have been many studies conducted on the effects on the water environment. The biggest sources of mercury pollution include "agriculture, municipal wastewater discharges, mining, incineration, and discharges of industrial wastewater" all relatively connected to water.

Mercury exists in three different forms, and all three possess different levels of bioavailability and toxicity. The three forms include organic compounds, metallic elements, and inorganic salts. As stated above, they are present in water resources such as oceans, rivers and lakes. Studies have shown that mercury turns into methylmercury (MeHg) and seeps into the environment. Plankton then get the metal into their system, and they are then eaten by other marine organisms. This cycle continues up the food web. This process is called They are absorbed by microorganisms, and going through, "biomagnification and causing causes significant disturbance to aquatic lives."

Mercury hurts marine life but can also be very hurtful towards humans' nervous system. Higher levels of mercury exposure can change many brain functions. It can "lead to shyness, tremors, memory problems, irritability, and changes in vision or hearing." '''Furthermore, breathing in mercury can lead to dysfunction in sensory and mental capabilities in humans as well such as with the use of one's motor skills, cognition, and sight. '''

'''Because of these worrying side effects, there was a study done in the Pacific coast of Columbia to assess the levels of mercury in the environment and in the people living there from gold-mining. The researchers found that the median total mercury concentration in hair measured from people living in two communities, Quibdo and Paimado, was 1.26$$\mu$$g/g and 0.67 $$\mu$$g/g respectively. Residents in other areas of Columbia have been found to have similar levels. These levels are greater than the recommended threshold values held by the U.S. Environmental Protection Agency (EPA). In addition, they measured the concentration of mercury found in fish living nearby in the Atrato River. Even though the concentration was determined to have a low risk factor for human health and consumption, the concentration (0.5 g/g) was above the World Health Organization's (WHO) recommended threshold.'''

They also determined that approximately 44% of the total sites around the river had a moderate level of pollution, further emphasizing that more intervention programs should be conducted to curb the seepage of mercury into the environment. This was a major concern especially since the Choco region is a biodiversity hotspot for all manner of organisms, not just humans. In the end, the highest levels of total airborne mercury were found to be in the gold shops downtown, further emphasizing the cost of gold-mining in such native communities and the need for better programs directed towards preventing its spread.

Pesticides

Pesticides are a major source of environmental toxicity. These chemically synthesized agents have been known to persist in the environment long after their administration. The poor biodegradability of pesticides can result in bioaccumulation of chemicals in various organisms along with biomagnification within a food web. Pesticides can be categorized according to the pests they target. Insecticides are used to eliminate agricultural pests that attack various fruits and crops. Herbicides target herbal pests such as weeds and other unwanted plants that reduce crop production.[citation needed]

Pesticides in general have been shown to negatively impact the reproductive and endocrine systems of various reptiles and amphibians, so much that it is cautiously thought to be one of the main factors behind the decline in their populations all over the world. These pesticides impair their immune, nervous, behavioral systems including causing lower fertility rates, abnormal hormone levels, and lower fitness of offspring. Amphibians are thought to be especially in low decline because the release of agricultural pesticides is simultaneous with the secretion of pheromones during their season of reproduction. For instance, it has been demonstrated that greater quantities of pesticides correlates with greater number of defects in toads.

For example, the chloroacetanilide class of herbicides is used worldwide in the control of weeds and grasses for agriculture. They are mainly used for crops such as corn, rice, soybean, sunflower, cotton, among others and are able to stay in the environment for long periods of time. Thus they can be found in soil, groundwater, and surface water due to soil erosion, leaching, and surface runoff. The amount of time they stay in the environment depends on the soil type and climate conditions like temperature and moisture. Chloroacetanilide herbicides include acetochlor, alachlor, among others. They are all listed as B2, L2, and C classes of carcinogens by the U.S. EPA.

Another herbicide called atrazine is still commonly used throughout the world even with the European Union banning its usage in 2005. Shockingly, its use was still prevalent in the U.S. in 2016 and in Australia for some time. Because it can dissolve in water, many concerns have been raised about its potential to contaminate soil and water along the surface and ground. Various studies have been conducted to determine the impact of atrazine on wildlife.

For example, studies have shown it to cause stunted growth and suppress or damage the immune and reproductive systems of aquatic life. It also is linked to cancer not only in fish, but also in mammals like humans. Additionally, atrazine is known to induce aromatase which causes the bodies of fish and amphibians to produce estrogen even when they are not supposed to. The herbicide also causes changes in gene expression which can be passed down from parent to offspring and get in the way of thyroid homeostasis. For example, a study done on male African clawed frogs show that exposure to atrazine led to smaller testicular size and lower testosterone levels. Another study done with the Northern leopard frog and Blanchard's cricket frog found that atrazine lowered their success with metamorphosis, the process of turning into an adult frog from the initial stage of a tadpole. This makes sense since metamorphosis is controlled by hormones from the thyroid gland which atrazine is known to negatively impact.

Furthermore, a study was done to study the effects of atrazine on freshwater crayfish Cherax destructor from the Czech Republic, a keystone species. They found that the hepatopancreas, the body part that serves as both the liver and pancreas in these crustaceans, became damaged after being exposed. A build-up of lactate and ammonia also resulted, leading to liver failure, tissue hypoxia, lactic acidosis, muscle fatigue, and pain. There was also damage and even deterioration of the gills however they were able to heal after 2 weeks. Damage to gills was also found in the bivalve Diplodon expansus.

PFAS chemicals

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Lawsuits around the world have now sprung up against companies and governments who knew of the harm these chemicals could do and continued to use them. Regulation talks on these chemicals is now happening world-wide. Remediation of these "forever chemicals" has been attempted in hot spots around the world, by placing the contaminated soil in landfill or heating at extremely high temperature. However, these are both very expensive, and new, cheaper remediation tools are desperately required.

Organophosphate chemicals

'''Organophosphate pesticides (OPs) are ester derivatives of phosphorus. These substances are found in pesticides, herbicides, and insecticides and were generally thought to be safe because they degrade quickly in the natural environment assuming there is sunlight, air, and soil. However, studies have shown these pesticides to negatively affect photosynthesis and growth in plants. These substances also get into the soil via runoff and cause decreases in soil fertility as well. Moreover, they have also been known to cause erratic swimming, respiratory stress, changes in behavior, and delayed metamorphosis in aquatic organisms. '''

'''In a specific case study, organophosphate pesticides like chlorpyrifos, diazinon, fenitrothion, and quinalphos used in agriculture in the northwestern part of Bangladesh were found to have high or acute ecological risks on the surface water and soil for aquatic insects and crustaceans. More specifically, it showed higher ecological risks for Daphnia compared to other marine organisms. The discovery of such high concentrations of pesticides could be due to the local farmers using more pesticides than the recommended amount. This could be due to agriculture being the country's biggest economical activity. With the country's rising population numbers, necessity for more food will only increase, thereby putting more pressure on farmers. '''