3.1: Environmental Chemicals
Aim: This section should help in understanding, general chemicals which are present in the environment, their sources and impacts.
“Environmental chemicals refer to a chemical compound or chemical element present in air, water, food, soil, dust, or other environmental media such as consumer products”. as per CDC (Centre for Disease control)
Living beings have always been exposed to chemicals in our environment - natural products in foods, smoke from cooking fires, sewage in drinking water, pesticides from plants. However, the dramatic increases in industrialization over the past three centuries have dramatically changed both the quality and the quantity of human exposures, to both natural and synthetic chemicals. We all know that certain things are bad for us - cigarette smoke, alcohol, lead, ozone (too much - or too little). But what about other substances in our environment such as gasoline fumes, dry cleaning fluids, pesticides, wood smoke, heavy metals?
Environmental health threats may come from physical agents, e.g., UV or ionizing radiation, or biologicals, such as mold, insects, bacteria, and viruses, as well as chemicals. Common environmental chemical pollutants include pesticides and herbicides, volatile organics (VOCs) such as benzene, toluene; and chloroform, heavy metals such as lead, mercury, and arsenic; air contaminants such as carbon monoxide, ozone, particulate matter (PM), and second hand smoke; and persistent organic pollutants, such as the dioxins, PCBs, and DDT. Environmental chemicals can cause a broad spectrum of effects, which depend not only on route of exposure and dose, but on the susceptibility of the recipient of the pollution. Age, gender, and genotype can have major effects on whether or not an exposure causes a problem. We know that children are not little adults, both as to behaviors, metabolism, and responses. We also know that the elderly may be a population at special risk to environmental chemicals. As is true from the study of pharmaceutical agents, much of our knowledge about the effects of environmental chemicals come from studies in animals. However, by using biomarkers of exposure and effect, as well as studies from some unfortunate poisoning episodes, we do have human information on many types of environmental exposures. Since nature is inherently conservative, when environmental chemicals cause multiple effects in multiple species, it is highly likely that people are also susceptible. Note: a biomarker is a substance that is measured in a biological system and an indicator of exposure, effect, susceptibility or clinical disease.
Various heavy metals such as lead, chromium, and cadmium contaminated agricultural soil, entering farm operations through application of sewage sludge as fertilizer, and the use of metal-based pesticides. The agricultural sector is also the world’s largest user of antibiotics, using 70 per cent of all that is manufactured. Overuse of pharmaceutical products (antibiotics and antimicrobial agents) – both in human medicine and veterinary practice – may contribute to creating resistant strains of microbes in humans, posing serious threats to health. Children are particularly susceptible to the negative health impacts of chemicals. Impacts on mental health are particularly significant. For example, mercury and lead exposure in utero and early in life can result in mental retardation, seizures, vision and hearing loss, and delayed development. The consumption of fish contaminated with methyl mercury is by far the most significant source of mercury exposure in humans - see Methylmercury Exposure and Health Effects.
3.1.1 Routes of Exposure:
Pollutants enter the human body in four main different ways: by inhalation, ingestion, skin absorption & Injection. The amount of any given pollutant that is received is often termed the dose. The dose will be dependent on the duration and intensity of the exposure. In many cases, exposure may occur simultaneously from many sources and through multiple routes. Pathways of exposures to lead, for example, include air pollution from traffic and industrial emissions, drinking water, food, tobacco smoking, dusts, paints and other industrially produced commodities and soil. People are often exposed to different pollutants simultaneously. Exposure to these may occur at different locations (e.g. in the workplace and/or at home) and at different times.
• Inhalation: For most chemicals in the form of vapors, gases, mists, or particulates, inhalation is the major route of entry. Once inhaled, chemicals are either exhaled or deposited in the respiratory tract. If deposited, damage can occur through direct contact with tissue or the chemical may diffuse into the blood through the lung-blood interface. Upon contact with tissue in the upper respiratory tract or lungs, chemicals may cause health effects ranging from simple irritation to severe tissue destruction. Substances absorbed into the blood are circulated and distributed to organs that have an affinity. Health effects can then occur in the organs, which are sensitive to the toxicant.
• Absorption through Skin (or eye): Skin (dermal) contact can cause effects that are relatively innocuous such as redness or mild dermatitis; more severe effects include destruction of skin tissue or other debilitating conditions. Many chemicals can also cross the skin barrier and be absorbed into the blood system. Once absorbed, they may produce systemic damage to internal organs.
• Ingestion: Chemicals that inadvertently get into the mouth and are swallowed do not generally harm the gastrointestinal tract itself unless they are irritating or corrosive. Chemicals that are insoluble in the fluids of the gastrointestinal tract (stomach, small, and large intestines) are generally excreted. Others that are soluble are absorbed through the lining of the gastrointestinal tract. They are then transported by the blood to internal organs where they can cause damage.
• Injection: Substances may enter the body if the skin is penetrated or punctured by contaminated objects. Effects can then occur as the substance is circulated in the blood and deposited in the target organs. Once the chemical is absorbed into the body, three other processes are possible: metabolism, storage, and excretion. Many chemicals are metabolized or transformed via chemical reactions in the body. In some cases, chemicals are distributed and stored in specific organs. Storage may reduce metabolism and therefore, increase the persistence of the chemicals in the body.
The production and use of chemicals continues to grow worldwide, particularly in developing countries. This is likely to result in greater negative effects on health if sound chemicals management is not ensured. Multisectoral action is urgently needed to protect human health from the harmful effects of improperly managed chemicals.
Following are some of the chemicals or groups of chemicals of major public health concern, taken from 10 chemicals of major public health concern.
Arsenic Soluble inorganic arsenic is acutely toxic. Intake of inorganic arsenic over a long period can lead to chronic arsenic poisoning (arsenicosis). Effects, which can take years to develop depending on the exposure level, include skin lesions, peripheral neuropathy, gastrointestinal symptoms, diabetes, renal system effects, cardiovascular diseases, and cancer. Organic arsenic compounds, which are abundant in seafood, are less harmful to health, and are rapidly eliminated by the body. Human exposure to elevated levels of inorganic arsenic occurs mainly through the consumption of groundwater containing naturally high levels of inorganic arsenic, food prepared with this water, and food crops irrigated with high arsenic water sources. In one estimate, arsenic-contaminated drinking-water in Bangladesh alone was attributed 9,100 deaths and 125,000 Disability Adjusted Life Years (DALYs) in 2001. Reduction in human exposure to arsenic can be achieved by screening of drinking-water supplies, clearly identifying those delivering water above the WHO guideline 10 µg arsenic per litre or national permissible limits, together with awareness-raising campaigns. Mitigation options include use of alternative groundwater sources, use of microbiologically safe surface water (e.g. rainwater harvesting), or use of arsenic removal technologies.
Asbestos: Asbestos All types of asbestos can cause lung cancer, mesothelioma, cancer of the larynx and ovary, and asbestosis (fibrosis of the lungs). Exposure to asbestos occurs through inhalation of fibres in air in the working environment, ambient air in the vicinity of point sources such as factories handling asbestos, or indoor air in housing and buildings containing friable (crumbly) asbestos materials. Currently about 125 million people in the world are exposed to asbestos at the workplace. In 2004, asbestos-related lung cancer, mesothelioma and asbestosis from occupational exposures resulted in 107,000 deaths and 1,523,000 DALYs. In addition, several thousands of deaths can be attributed to other asbestos-related diseases, as well as to nonoccupational exposures to asbestos. Elimination of asbestos-related diseases should take place through the following public health actions: a) recognizing that the most efficient way to eliminate asbestos-related diseases is to stop the use of all types of asbestos; b) replacing asbestos with safer substitutes and developing economic and technological mechanisms to stimulate its replacement; c) taking measures to prevent exposure to asbestos in place and during asbestos removal (abatement), and; d) improving early diagnosis, treatment, social and medical rehabilitation of asbestos-related diseases and establishing registries of people with past and/or current exposures to asbestos.
Benzene: Human exposure to benzene has been associated with a range of acute and long term adverse health effects and diseases, including cancer and aplastic anaemia. Exposure can occur occupationally and domestically as a result of the ubiquitous use of benzene-containing petroleum products including motor fuels and solvents. Active and passive exposure to tobacco smoke is also a significant source of exposure. Benzene is highly volatile and exposure occurs mostly through inhalation. Interventions to reduce both work and general population exposure include promoting the use of alternative solvents in industrial processes, developing and implementing policies and legislation to remove benzene from consumer products, discouraging domestic use of benzene-containing products, stopping smoking, and promoting building codes requiring detached garages.
Cadmium: Cadmium exerts toxic effects on the kidney, the skeletal and the respiratory systems, and is classified as a human carcinogen. It is generally present in the environment at low levels; however, human activity has greatly increased those levels. Cadmium can travel long distances from the source of emission by atmospheric transfer. It is readily accumulated in many organisms, notably molluscs and crustaceans. Lower concentrations are found in vegetables, cereals and starchy roots. Human exposure occurs mainly from consumption of contaminated food, active and passive inhalation of tobacco smoke, and inhalation by workers in the non-ferrous metal industry. Interventions to reduce global environmental cadmium releases and occupational and environmental exposure include increased recycling of cadmium, minimizing emissions and discharges from activities such as mining and waste management, promoting safe working conditions for workers manipulating cadmium containing products, and stopping smoking.
Dioxins & dioxin-like substances: Dioxins and dioxin-like substances, including PCBs, are persistent organic pollutants (POPs) covered by the Stockholm Convention. They can travel long distances from the source of emission, and bioaccumulate in food chains. Human exposure to dioxins and dioxin-like substances has been associated with a range of toxic effects, including immunotoxicity, developmental and neurodevelopmental effects, and changes in thyroid and steroid hormones and reproductive function. Developmental effects are the most sensitive toxic endpoint making children, particularly breast-fed infants, the population most at risk. These substances are byproducts of combustion and various industrial processes, such as chlorine bleaching of paper pulp and smelting. While manufacture of PCBs should have been discontinued, release into the environment still occurs from disposal of large scale electrical equipment and waste. Human exposure to dioxin and dioxin-like substances occurs mainly through consumption of contaminated food.
Fluoride: Inadequate or excess fluoride Fluoride intake has both beneficial effects – in reducing the incidence of dental caries – and negative effects – in causing enamel and skeletal fluorosis following prolonged high exposure. The ranges of intakes producing these opposing effects are not far apart. Public health actions are needed to provide sufficient fluoride intake in areas where this is lacking, so as to minimize tooth decay. This can be done through drinking water fluoridation, or, when this is not possible, through salt or milk fluoridation. Excessive fluoride intake usually occurs through the consumption of ground water naturally rich in fluoride, or crops that take up fluoride and are irrigated with this water. Such exposure may lead to crippling skeletal fluorosis, which is associated with osteosclerosis, calcification of tendons and ligaments and bone deformities. While the global prevalence of dental and skeletal fluorosis is not entirely clear, it is estimated that excessive fluoride concentrations in drinking water have caused tens of millions of dental and skeletal fluorosis cases world-wide over a range of years. Although removal of excessive fluoride from drinking-water may be difficult and expensive, low-cost solutions that can be applied at a local level do exist. It is important that local authorities consider the causes of fluorosis carefully and choose the best and most appropriate means of dealing with excess fluoride exposure taking into account the local conditions and sensitivities.
Lead: Lead is a toxic metal whose widespread use has caused extensive environmental contamination and health problems in many parts of the world. It is a cumulative toxicant that affects multiple body systems, including the neurologic, hematologic, gastrointestinal, cardiovascular, and renal systems. Children are particularly vulnerable to the neurotoxic effects of lead, and even relatively low levels of exposure can cause serious and in some cases irreversible neurological damage. Lead exposure is estimated to account for 0.6% of the global burden of disease, with the highest burden in developing regions. Childhood lead exposure is estimated to contribute to about 600,000 new cases of children with intellectual disabilities every year. Recent reductions in the use of lead in petrol, paint, plumbing and solder have resulted in substantial reductions in blood lead levels. However, significant sources of exposure still remain, particularly in developing countries. Further efforts are required to continue to reduce the use and releases of lead and to reduce environmental and occupational exposures, particularly for children and women of child-bearing age. Interventions include eliminating non-essential uses of lead such as lead in paint, ensuring the safe recycling of lead-containing waste, educating the public about the importance of safe disposal of lead-acid batteries and computers, and monitoring of blood lead levels in children, women of child-bearing age and workers.
Pesticides: Highly hazardous pesticides Highly hazardous pesticides may have acute and/or chronic toxic effects, and pose particular risk to children. Their widespread use has caused health problems and fatalities in many parts of the world, often as a result of occupational exposure and accidental or intentional poisonings. Available data are too limited to estimate the global health impacts of pesticides, however the global impact of self-poisoning (suicides) from preventable pesticide ingestion has however been estimated to amount to 186,000 deaths and 4,420,000 DALYs in 2002. Environmental contamination can also result in human exposure through consumption of residues of pesticides in food and, possibly, drinking water. While developed countries have systems already in place to register pesticides and control their trade and use, this is not always the case elsewhere. Guidance and legal frameworks on the use, management and trade of pesticides, as well as proper storage and handling, are available from international organizations and international conventions; these should be implemented globally.
Case Study: Flint Michigan: On April 2014, the city of Flint, Michigan has decided to switch water sources from Lake Huron to the Flint River in order to save money. After switching water sources, the local people started to complain about the odour and smell of the water. As a result, toxic lead started to contaminate the water due to the aging lead pipes, leading to many illnesses among local residents. Please take a look at this infographic by the Keck School of Medicine of USC to see the timeline of the Flint Water crisis.