PRINCIPLES OF ENVIRONMENTAL TOXICOLOGY AND CONTAMINATION (PART I)

Table of Contents

1. Index
2. UNIT 1 - General principles
3. UNIT 2 - Main sources of environmental contamination
4. UNIT 3 - Air Pollution
5. Unit 4 - Water and soil Pollution
   1. Introduction
   2. Sources of Water and Soil Pollutants
   3. Examples of Water and Soil Pollutants and their Environmental and human health effects
   4. Other Environmental and human health effects of water pollution
   5. Other environmental and human health effects of soil pollution
6. Glossary of key terms associated with environmental toxicology

Examples of Water and Soil Pollutants and their Environmental and human health effects

Metals that are of environmental concern fall into three classes:

• Metals that are suspected carcinogens;
• Metals that move readily in soil;
• Metals that move through the food chain.

The heavy metals of greatest concern for health with regard to drinking water exposure are lead and arsenic.

Lead - The most important sources of lead in drinking water are from lead solder and lead pipes. Also of concern is the seepage of lead from the soil contaminated with the fallout from leaded gasoline and seepage of lead from hazardous waste sites. Lead poisoning has been common in children, particularly in older housing units and inner city dwellings, in which children may consume chips of lead contaminated paint. If lead enters the human body system in higher quantities it affects the reproductive and nervous system - lead is a neurological poison when high amounts are ingested -, the red blood cells (RBCs) and many organs like bones, brain, liver, kidneys. Numbness, seizures, paralysis, insomnia, stomach distress, and constipation are symptoms of lead toxicity. Severe lead poisoning can also cause coma and death. More information on lead and its toxic effects can be found in unit 3.

Arsenic - Drinking water is at risk for contamination by arsenic (a toxic metalloid) from the leaching of inorganic arsenic compounds formerly used in pesticide sprays, from the combustion of arsenic-containing fossil fuels, and from the leaching of mine tailings and smelter runoff. Chronic high-level exposures can cause abnormal skin pigmentation, hyperkeratosis, abdominal pain, and nasal congestion. At lower levels of chronic exposure, cancer is the major concern. Epidemologic studies have linked chronic arsenic exposure to various cancers, including lungs, skin, and lymph glands. In addition, arsenic poisoning can also cause death, liver and kidney disorders (e.g. renal failure), nervous disorders and muscular atrophy.

More information on arsenic and its human health effects can be found in the following link:

http://www.who.int/mediacentre/factsheets/fs372/en/

Cadmium - This metal is typically found in ores with other metals, and is commercially produced as a by-product of zinc and lead smelting, which are sources of environmental cadmium. Fertilizers are also a source of cadmium pollution. If cadmium enters the human body, it gets deposited in visceral organs such as pancreas, liver, kidney, intestinal mucosa, etc. Cadmium poisoning causes headache, vomiting, bronchial pneumonia, kidney necrosis, etc.

In the 1960s, mining wastes were dumped into rice paddies in Japan. The chemicals present in the mining wastes dissolved into the water in the rice paddies, and were also absorbed into the rice itself. Middle-aged women with calcium-deficient diets and multiple pregnancies began developing a set of symptoms that included lumbago, extreme bone pain, pain in the back, shoulders, and joints, a waddling gait, frequent bone fractures, elevated levels of calcium and protein in their urine and consequently, severe kidney damage. This set of symptoms was called itai-itai (ouch-ouch disease) because of the pain associated with walking. It was later determined that the causative agent of this disease was cadmium that was present in high levels in the mining wastes. The middle-aged women that developed this disease had a daily cadmium intake about two hundred times the typical intake in an unpolluted area. Therefore, this contamination resulted from irrigation of the soil with water containing cadmium released from industrial sources. Similarly, cadmium toxicity in Japan also resulted from consumption of cadmium-contaminated fish taken from rivers near smelting plants. It is known that one of the most significant effects of metal pollution is that aquatic organisms can accumulate metals in their tissues, leading to increased concentrations in the food chain.

Concern about long-term exposure to cadmium intensified after recognition of the disease Itai-Itai (painful-painful). 

More information on cadmium (e.g. sources) and its health hazard can be found in the following link:

http://www.epa.gov/ttnatw01/hlthef/cadmium.html

Mercury - This metal is released into the atmosphere from a variety of natural and anthropogenic sources. Natural sources include volcanoes, soils, forests, lakes, and open oceans. Anthropogenic sources mainly result from combustion processes (e.g. combustion of coal) and waste incineration. Elevated levels of mercury exist in waters that are remote from anthropogenic emission sources, which indicates that atmospheric deposition is also an important source of contamination. Although it is difficult to identify atmospheric deposition sources in remote regions, it is generally accepted that anthropogenic-based emissions have greatly increased relative to natural sources since the start of industrialization.

Mercury is widely used in scientific and electrical apparatus, with the largest industrial use of mercury being in the chlorine-alkali industry for electrolytic production of chlorine and sodium hydroxide. Worldwide, this industry has been a major source of mercury contaminations. Additionally, metals like mercury are let off into water bodies from industries. As an example, in Japan in the 1950s and 1960s, wastes from a chemical and plastics plant containing mercury were discharged into Minamata Bay. In this industrial plant (near the Minamata Bay), the elemental form of mercury was used as a catalyst in the synthesis of acetaldehyde that is used in the manufacturing of plastics, perfumes, synthetic rubber, and other products. In the 1950s some people developed a specific set of neurotoxic symptoms (effects on the nervous system). Effects included narrowing of the visual field, speech impairment, neurological paresthesias and ataxia (loss of coordination). In 1963 the disease was identified as organomercurial poisoning, and later became known as Minamata's Disease.

Between 1965 and 1974, 520 patients at one location in Nigata were treated for this disease. All of these cases came from the mercury released from the plant. The cases were unexpected because the elemental form of mercury does not cause these effects. However, once the mercury was released into the water, the aquatic plant life and microbes (bacterial action) in the sediment of the bay converted the mercury, as part of their regular physiological functions, to an organic form - known as methylmercury - able to enter the nervous system. The methylmercury was then taken up by fish and shellfish that ate the plants or animals that lived in the sediments. Fish living in the contaminated waters of the Bay were consumed by larger fish. Over the years, through a process known as bioaccumulation (see chapter 5), methylmercury was incorporated progressively into animal tissues and the food chain. Moreover, the local population ate the fish and shellfish, and these people reported the toxic effects (neurologic symptoms). Even though the mothers appeared healthy, many infants born to these mothers who had eaten contaminated fish developed cerebral palsy-like symptoms, mental deficiency and developmental delays. Cases of intrauterine intoxication became known as "fetal Minamata disease". By 1970, at least 107 deaths had been attributed to mercury poisoning, and 800 cases of Minamata disease were confirmed. Methylmercury exposure also may cause hearing defects.

More information on mercury (e.g. sources) and its environmental and human health effects can be found in the following paper and link:

http://www.epa.gov/mercury/effects.htm

Pesticides are also a major source of concern as water and soil pollutants. Because of their persistence and stability, the most hazardous pesticides are the organochlorine compounds such as DDT (1,1,1-trichloro-2,2-di(4-chlorophenyl)ethane), dieldrin, aldrin, and chlordane. Persistent pesticides can accumulate in food chains; for example, fish and shrimp can concentrate some pesticides as much as 1000-10,000-fold, and consequently the aquatic environments can be adversely affected. This bioaccumulation has been well documented with the pesticide DDT, especially in raptorial birds (e.g., falcons). Therefore, due to the properties of DDT, their concentration in birds could be much higher than concentrations in insects or soil. Similarly, the highest concentrations of DDT in birds were observed at the top of the food chain (e.g., pelicans, falcons, eagles, and grebes). Although the amount of DDT did not kill the birds, it interfered with calcium metabolism, which led to thin eggshells. As a result, eggs would crack during development, allowing bacteria to enter, which killed the developing embryos. This had a great impact on the population levels of these birds. Peregrine falcons and brown pelicans were placed on the endangered species list in the United States, partially due to the declining reproductive success of the birds from DDT exposure. DDT is now banned in many parts of the world such as in Europe and United States.

In contrast to the persistent insecticides, the organophosphorus (OP) pesticides, such as malathion, and the carbamates, such as carbaryl, are short-lived and generally persist for only a few weeks to a few months. Therefore, these compounds do not usually present as serious a problem as the earlier insecticides. Herbicides, because of the large quantity used, are also of concern as potential toxic pollutants.

Pesticides can eventually cause death in most of the aquatic organisms. For more information about pesticides and their effects on environmental and human health, see the following document and link:

http://www.epa.gov/pesticides/health/human.htm#healtheffects

(on the left, click also in "pesticides home", or "environmental effects" and explore the link)

The increase in these nutrients, particularly phosphates, is of environmental concern because excess nutrients can lead to "algal blooms" or eutrophication, as it is known, in ponds, lakes, estuaries, and very slow moving rivers. The algal bloom reduces light penetration and restricts atmospheric reoxygenation of the water. When the dense algal growth dies, the subsequent biodegradation results in anaerobic conditions and the death of many aquatic organisms. Thus, low oxygen levels in the water (hypoxia) affect the natural ecological balance of watercourses (e.g. rivers, lakes). High phosphate concentrations and algal blooms are generally not a problem in moving streams, because such streams are continually flushed out and algae do not accumulate.

There are two potential adverse human health effects from nitrates in drinking water:

• Nitrosamine formation; certain nitrosamines are known carcinogens.
• Methemoglobinemia: Ingested nitrates can be converted to nitrites by intestinal bacteria. After entering the circulatory system, nitrite ions combine with hemoglobin to form methemoglobin, thereby decreasing the oxygen-carrying capacity of the blood and resulting in anemia or blue baby disease. It is particularly severe in young babies who consume water and milk formula prepared with nitrate-rich water. Older children and adults are able to detoxify the methemoglobin as a result of the enzyme methemoglobin reductase, which reverses the formation of methemoglobin. In infants, however, the enzyme is not fully functional.

Additional information about EDCs and their impacts can be found in the following articles and videos:

Videos: https://www.youtube.com/watch?v=qB-qA9KMsTE
https://www.youtube.com/watch?v=7of85pknFoI

Emerging Contaminants

"Emerging contaminants" can be broadly defined as any synthetic or naturally occurring chemical that is not commonly monitored in the environment but has the potential to enter the environment and to cause adverse ecological and/or human health effects. In some cases, release of emerging chemical to the environment has likely occurred for a long time, but may not have been recognized until new detection methods were developed. In other cases, synthesis of new chemicals or changes in use and disposal of existing chemicals can create new sources of emerging contaminants.

Pharmaceuticals and Personal Care Products (PPCPs) have been reported in water since the 80s. However, the number of studies that investigated the occurrence of PPCPs in the environment has only increased since the 90s, due to the continuous improvement in chemical analysis methodologies.

Although detected at low concentrations (ng/L or µg/L range), the recent knowledge of their occurrence has raised concerns about human health effects and ecosystem risks. While potential human exposure to contaminated water occurs in a discontinuous process, organisms in aquatic ecosystems are continually exposed to this type of contamination. Further, environmental monitoring studies have identified compounds that are present in some ecosystems at levels that can induce negative effects for organisms.

There is still a serious lack of information about the effects in non-target species particularly considering chronic exposure. Some PPCPs have been classified as Endocrine Disrupting Chemicals (EDCs) given their capacity to affect directly or indirectly endocrine systems in humans and wildlife, even at low concentrations. In many cases, negligible effects may occur from a continuous exposure during the entire life of organisms or a multi-generational exposure to low concentrations of PPCPs. These effects might be cumulative thus affecting the population and the ecosystem.

Moreover, even if these compounds are present below the No Observed Effect Concentration (NOEC), toxic effects due to a long-term exposure or to a combination of contaminants cannot be disregarded.

PPCPs enter in the environment from a different number of sources and pathways. Some compounds and their metabolites cannot be entirely used by organisms and are released into the water by excretion. Excretion of the compound or products resulting of its biotransformation, improper disposal of unused PPCPs in landfills or discharge into the collection system of wastewater, hospital effluents and septic tanks are some of possible pathways. On the other hand, waste resulting from pharmaceutical production, agricultural activities and industry effluents, as well as hospital, veterinary and aquaculture stations waste, contribute to their occurrence in wastewater, surface, groundwater and, at a lesser extent, in drinking water. There is no treatment in Wastewater Treatments Plants (WWTPs) that ensures complete removal of compounds, and so WWTPs effluents may still have significant concentrations of some PPCPs.

Different classes of pharmaceuticals have been detected in several ecosystems, including analgesic and anti-inflammatory drugs, β-blockers, steroids and related hormones, antibiotics, hypolipidemics and antiepileptics. These compounds are subject to restrict regulatory approval processes to evaluate the efficacy and safety, and studies are performed at doses close to the therapeutic dose. For this reason, pharmaceuticals have a substantial margin of safety and are better characterized than many others environmental contaminants.

Although pharmaceuticals have been designed to be bioactive in humans, aquatic organisms that present conserved signaling pathways can experience the same pharmacodynamics effects. Moreover, secondary effects that are less frequent in human treatments may be more relevant in aquatic organisms.

The primary classes of reported PCPs include disinfectants (e.g. triclosan, triclocarban), fragrances (e.g. musks), insect repellants (e.g. DEET), preservatives (e.g. parabens) and UV filters (e.g. methylbenzylidene camphor). Further, as many PCPs are designed for external use, they are not subjected to biotransformation in organisms and thus a large quantity of these unaltered compounds is released into the environment through regular usage.

For more information, consult the following papers:

Nanoparticles occur naturally and have been defined as particles that have one dimension that is less than 100 × 10^–9 mm. Of particular interest are engineered nanoparticles. Engineered nanoparticles (ENPs) are present in many industrial products, including certain paints, sprays, cosmetics, surface coatings, pesticides, and products for bioremediation of soils. The materials constituting ENPs are diverse (e.g. aluminum oxide, titanium oxide, silver, zinc oxide, cerium oxide, carbon). Nanoparticles of one kind or another are widely distributed across the global environment. Thus, a recently interest has grown in the possible toxic effects of small engineered particles.

It is known that there are two distinct ways in which nanoparticles may express ecotoxicity. One is by the toxic effects of the particles themselves by generating reactive radicals and the other is by acting as vectors for persistent pollutants. In this last case, the surface properties and very small size of nanoparticles provide surfaces that may bind and transport toxic chemical pollutants. There is a wealth of evidence for the harmful effects of nanoscale combustion-derived particulates (ultrafines), which when inhaled can cause a number of pulmonary pathologies in mammals and humans. However, there are many unanswered questions about the significance of global pollution by ENPs.

The effects of nanoparticles in the environment and human health can be found in the following review article and link:

http://ec.europa.eu/health/scientific_committees/opinions_layman/en/nanotechnologies/l-2/6-health-effects-nanoparticles.htm

Oils and petroleum are ever-present pollutants are ever-present pollutants in the modern environment, whether from the used oil of private motorists or spillage from oil tankers.

Effects...

Petroleum can cause environmental harm by toxic action, physical contact, chemical and physical changes within the soil or water medium, and habitat alteration.

Oil maritime incidents (e.g. spillages, fires, leakages, and explosion) can pose a significant threat to human health and marine and shoreline environments. The environmental impacts are often more obvious than human health effects (e.g. skin irritations, rashes, etc.), causing visible detriment to beaches, coastlines and wildlife. Generally, it is the aquatic species that are first exposed to chemicals released into surface water (e.g. lakes, rivers, and oceans) likely over a long period of time. On the other hand, oil can be deposited on rocks and sand, preventing the recreational use of beaches until after a costly clean up. Furthermore, maritime incidents can also cause economic losses from business interruption (e.g. loss of fishing and aquaculture resources).

Figure 2 - Oil impacts to the beach environment of Grand Isle, Louisiana. Oil and other chemicals can get into sediments, impacting large coastal areas, threatening human health, and reducing the economic well being of regions that depend on a healthy coastal environment. Source: NOAA (2015).

Oil does not dissolve in the water and forms a thick layer on the water surface. At sea, oil slicks are responsible for the deaths of many aquatic organisms. Mammals that rely on fur for insulation (polar bear, fur seals, otters, muskrat) are the most likely to die from oiling. Reptiles and amphibians can be killed by petroleum, but available information is inadequate to evaluate properly the sensitivity of these organisms to petroleum. Birds are often killed by oil spills, primarily because of plumage oiling (oil can stick to the bodies and feathers) and oil ingestion. Birds that spend much of their time on the water surface are the most vulnerable to spilled oil. Ingested oil can cause many sublethal effects, and transmittal to nests and eggs is highly embryotoxic. Very few birds that are badly contaminated recover, even after de-oiling and hand feeding.

Figure 3 - Oiled seabird unable to fly following a spill. 
Source: http://3wisemenessentials.com/petroleum_industry.html

Additionally, the oil spills can cause major changes in local plant and invertebrate populations lasting from several weeks to many years. For example, shore animals such as crabs, shrimps, mussels, and barnacles are also affected by the toxic hydrocarbons they ingest. Therefore, the ecosystems may take many years to recover from an incident, particularly when the chemicals involved are persistent, of low solubility and low volatility. Nevertheless, the subtle and perhaps potentially more harmful long-term effects on aquatic life are not yet fully understood. Additionally, the effects of oil spills on populations of mobile vertebrate species, such as fish, birds, and mammals, have been difficult to determine beyond the immediate losses in local populations.

One example...

One of the most famous incidents from the recent past is the large oil spill from the Exxon oil tanker near Valdez, Alaska. This oil tanker ran aground on a reef off the Alaskan coast, releasing gallons of crude oil into the sea. In this case, the toxicity was largely due to the thick oil that covered the wings of birds and fur of marine mammals (e.g. sea otters). This oil prevented birds from flying and prevented birds and mammals from regulating their body temperature. The oil entered the intertidal zones and was distributed across rocks, on beaches, and in the sediments. Because of the wide distribution of the oil, essentially all aquatic organisms, ranging across the food chain from algae to whales, were affected to some degree. The ecosystem in the area was greatly impaired by this spill.

More information on the impacts (economic, environmental, human health) of oil spills can be found in the following links:

http://www.itopf.com/knowledge-resources/documents-guides/environmental-effects/

http://oils.gpa.unep.org/facts/economy-health.htm

HNS - is defined as a substance other than oil which if introduced into the marine environment is likely to create hazards to human health, to harm living resources and marine life, to damage amenities or to interfere with other legitimate uses of the sea. Information on HNS (e.g. human and environmental effects, etc.) can be found in the following link and documents:

http://www.itopf.com/knowledge-resources/documents-guides/hazardous-and-noxious-substances-hns/

(Explore the documents on HNS in the link)

PAHs - Natural sources of polyaromatic hydrocarbons (PAHs) in the environment include forest and grass fires, volcanoes, oil seeps, and plants. Anthropogenic sources of PAHs include petroleum spills and discharges, refuse incineration, electric power generation, home heating, and internal combustion engines.

Aquatic contamination by PAHs is caused by petroleum spills, discharges, and seepages, industrial and municipal wastewater, urban and suburban surface runoff, and atmospheric deposition. The primary mechanism for atmospheric contamination by PAHs is the incomplete combustion of organic matter which may occur both through natural processes (e.g. forest fires) and through anthropogenic activities (e.g. combustion of coal for energy production, cigarette smoking). PAHs are also present in smoke released from chimneys.

Many PAHs are known to cause lung and skin cancer in animals, and likely cause these cancers in humans. Additionally, the induction of lesions and neoplasms in laboratory animals by metabolites of PAHs and observations of lesions and neoplasms in fish from PAH-contaminated sites indicate potential health problems for animals with cytochrome P-450 capable of metabolizing PAHs. Although evidence linking environmental PAHs to the incidence of cancerous neoplasms in wild animals is limited and primarily circumstantial, the growing quantities of PAHs entering the environment are a cause of concern.

More information on polycyclic aromatic hydrocarbons (PAHs), their uses, sources and environmental and human health effects can be found in the following link and article and also at the Arcopol Platform project website (http://www.arcopol.eu/ ):

http://www.toxipedia.org/display/toxipedia/Polycyclic+Aromatic+Hydrocarbons

VOCs are common groundwater contaminants. They include halogenated solvents and petroleum products, collectively referred to as VOCs. Both groups of compounds are used in great quantities by a variety of industries, such as dry cleaning, degreasing, paint, and the military. Historically, petroleum products were stored in underground tanks that would erode, or were spilled onto soil surfaces. The EPA's National Priority List includes 11 VOCs: benzene; chloroform; dichloromethane; ethylbenzene; tetrachloroethylene; toluene; 1,1,1-trichloroethane; trichloroethylene; trans-1,2-dichloroethane; vinyl chloride; and xylene.

The chemical and physical properties of VOCs permit them to move rapidly into groundwater, and almost all of the previously mentioned chemicals have been detected in groundwater near contaminant sites. High levels of exposure can cause impaired cognition, headache, and kidney toxicities. At levels of exposure most frequently encountered, cancer and reproductive effects are of utmost concern, particularly childhood leukemia.

Low molecular weight chlorinated hydrocarbons are a by-product of the chlorination of municipal water. Chlorine reacts with organic substances commonly found in water to generate trihalomethanes (THMs), such as chloroform. The main organics that have been detected are chloroform, bromodichloromethane, bromoform, carbon tetrachloride, dibromochloromethane, and 1,2-dichloroethane. These compounds are associated with an increased risk of cancer. Studies in New Orleans in the mid-1970s showed that tap water in New Orleans contained more chlorinated hydrocarbons than untreated Mississippi River water or well water. Additionally, chlorinated hydrocarbons, including carbon tetrachloride, were detected in blood plasma from volunteers who drank treated tap water. Epidemiologic studies indicated that the cancer death rate was higher among males who drank tap water than among those who drank well water.

Radioactive contamination as background radiation from natural sources, such as radon, occurs in some regions of the world, but there is particular concern over the contamination of surface water and groundwater by radioactive compounds generated by the processing of nuclear fuel and by the production of nuclear weapons. Water pollution due to the nuclear wastes disposal will affect the marine animals. This kind of water if consumed by humans can cause a series of dreadful diseases like cholera, typhoid, jaundice, gastroenteritis, etc. The effect of this type of water pollution on growing foetus is very dangerous in pregnant women. It causes delayed or incomplete mental development, autism or brain damage in foetus.

The term VOCs also encompasses other compounds such as organic acids. Acids present in rain or drainage from mines are main pollutants in many freshwater rivers and lakes. Because of their ability to lower the pH of the water to toxic levels and release toxic metals into solution, acids are considered particularly hazardous.

The number of organic compounds found as water and soil contaminants continues to grow each year. They include polychlorinated biphenyls (PCBs), phenols, cyanides, plasticizers, solvents, and numerous industrial chemicals. PCBs were historically used as coolants in electrical transformers and are also known by-products of the plastic, rubber, lubricant, and paper industries. They are stable, lipophilic, and break down only slowly in tissues. Because of these properties, they accumulate to high concentrations in fish and waterfowl. In 1969, PCBs were responsible for the death of thousands of birds in the Irish Sea.

More information on PCBs and their health effects can be found in the following link:

http://www.epa.gov/epawaste/hazard/tsd/pcbs/index.htm

Dioxins - have contaminated large areas of water and soil, most notably with the extremely toxic TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) through industrial accidents and through widespread use of the herbicide 2,4,5-T. Small amounts of TCDD were contained as contaminants in herbicide manufacturing. TCDD is one of the most toxic synthetic substances known for laboratory animals: lethal dose 50 (LD₅₀) for male rats is 0.022 mg/kg; LD₅₀ for female rats is 0.045 mg/kg; and LD₅₀ for female guinea pigs (the most sensitive species tested) is 0.0006 mg/kg. Furthermore, it is fetotoxic to pregnant rats at a dose of only 1/400 of the LD₅₀ and has been shown to cause birth defects at levels of 1-3 ng/kg. TCDD is a proven carcinogen in both mice and rats, with the liver being the primary target. Although TCDD does not appear to be particularly acutely toxic to humans, chronic low-level exposure is suspected of contributing to reproductive abnormalities and carcinogenicity.

Example of an accident with dioxins:

In July 1976, an accident captured much public attention due to the release of several kilograms of dioxin into the atmosphere and soil at Seveso, Italy. The release was related to the production of trichlorophenol at a plant about twenty miles north of Milan. The resulting toxic cloud of vapours released from the plant contaminated several thousand acres of a densely populated area of Seveso. Vegetation, birds, and animals near the plant were affected within days of the release. Many herbivorous animals (e.g. rabbits, sheep) died from eating contaminated plants. Nine days after the release, dioxins were found to be present in the plants, animals, and soils of the area. Skin lesions (known as chloracne) were reported by residents, especially in children who had more direct contact with the contaminated soils than adults. Overall, the accident was considered directly responsible for the deaths of about 3,300 small animals, and about a dozen domestic animals.

More information on dioxins and their health effects can be found in the following links and video:

http://www2.epa.gov/dioxin/learn-about-dioxin

http://www.who.int/mediacentre/factsheets/fs225/en/

Video: https://www.youtube.com/watch?v=n3gjUPdfmHQ

The problem of plastic pollution and microplastics

Most plastic debris originates from ocean-based sources such as waste from cruise ships or fishing gear from the fishing industry. Ship-generated debris is the major source of marine debris found on remote shores. However, in highly populated areas, land-based sources dominate the input of plastic waste into the marine environment.

The properties that make plastics such desirable materials for modern society can make them lethal for wildlife, when introduced into the environment. Numerous species (e.g. sea turtles, seabirds, marine mammals, fish, crustaceans, etc.) are affected by plastic pollution, primarily because organisms become entangled in plastic nets, or plastic objects are ingested when organisms mistake plastic debris for food. Entanglement can cause death by drowning, suffocation, strangulation, or starvation. Very often, birds, turtles, small whale species, and seals drown in ghost nets or old fishing gear, lose their ability to catch food, or cannot avoid predators because of their entanglement.

Figure 4 - A Grey Seal inside a seal shelter at Texel, The Netherlands. The seal was entangled in a nylon thread which cut their flesh and damaged the backbone. It suffered from internal bleeding and symptoms of paralysis. Because of its incurable injuries the veterinarian euthanized this animal. Source: Hammer et al. (2012).

Another problem of plastic pollution is that it facilitates the transport of species to other regions; alien species hitchhike on floating debris and invade new ecosystems, thereby causing a shift in species composition or even extinction of other species.

Plastics are considered to be biochemically inert; because of their macromolecular structures, they neither react with, nor penetrate the cell membrane of an organism. However, most plastics are not pure. Besides their polymeric structure, they consist of a variety of chemicals that all contribute to a certain property of the plastics. These chemicals are called additives (e.g.Phthalates, Bisphenol A (BPA), Brominated flame retardants (BFRs)). Additives are mostly of small molecular size, are often not chemically bound to a polymer and are, therefore, able to leach from the plastics into the environment. Being primarily liphophilic, they penetrate cell membranes, interact biochemically, and cause toxic effects.

Phthalates and BPA are examples of toxic additives. These agents can affect reproduction, impairing development, and induce genetic aberrations in a variety of organisms. Therefore, phthalates and BPA disrupt the functioning of the hormone system (are proven endocrine disruptors), and have received much attention because of their ubiquitous presence in the environment and in humans. On the other hand, some BFR congeners cause reproductive and carcinogenic effects, disrupt endocrine systems, and cause neurotoxicological effects on mammals and aquatic organisms.

Moreover, plastic debris in the marine environment not only contain additives, but also contain hydrophobic chemicals (contaminants) adsorbed from the surrounding water. Thus, the hydrophobic surface of plastics has an affinity for various hydrophobic contaminants, and these accumulate on, and in the plastic debris. This mechanism receives great attention for microdebris or microplastics, because they are easily ingested by organisms and thereby, constitute a pathway for chemicals to enter in an organism as small as plankton (plankton species form the foundation of every food web). This causes a threat to the basis of the marine food web and can have serious and far-reaching effects, even on nonmarine species such as humans. Hence, the ingestion of plastics could play a significant role in the accumulation of contaminants by marine organisms. Plastics not only adsorb and transport contaminants in the environment, but may also increase their environmental persistency.

More information on plastic pollution can be found in the following links:

http://plastic-pollution.org/

http://plasticpollutioncoalition.org/

(see the video)