Drinking Water Quality
The supply of clean, safe drinking water is becoming less reliable in many parts of the world. Poor quality water is the world's greatest health problem. Water quality is affected by many sources of contamination and over-exploitation.
Polychlorinated biphenyls (PCBs) are a group of compounds once commonly used in a broad range of industrial applications, including as dielectric fluids and coolants in electrical devices, such as transformers, motors, and capacitors. Highly toxic and carcinogenic, and bio-accumulating. Regulated by the Stockholm Convention on POPs (2001).
The general formula is C12H10-xClx. The common pattern consists of 2 benzene rings with a variable number of chlorine atoms, in 209 known configurations, of which 130 have been used commercially.
PCBs have low water solubilities (0.0027-0.42 ng/L), and high solubility in organic solvents, including organic tissue, oil and and fat. PCBs have a low vapour pressure at room temperatures, high thermal conductivitiy, and are resistent to chemical decomposition, such as oxidation, reduction , addition , elimination and electrophilic substitution.
Polychlorinated biphenyls are chemically extremely stable, have low flammability, and are electrically insulating, making them ideal for use as dielectric and coolant fluids in electrical and electronic devices. Transformers and capacitors are filled of PCBs, requiring their disposal to be undertaken as special waste.
Their applications are broadly classified as 'open' and 'closed', the latter being sealed from the environment inside a casing. Open applications include as carbonless copy paper (NCR), plasticizers in paints and cements, stabilizing additives in flexible PVC coatings of electrical cables and electronic components, flame retardants and sealants, adhesives, flooring finishers, and water-proofing compounds. One particularly hazardous application was in coal tars used in waterproofing drinking water tanks.
The paths of PCB transfer are complex and global in scale. Despite their hydrophobicity, PCBs the main reservoir of the pollutants is the hydrosphere, although the primary route of global transport is air (especially cogeners with 1-4 chlorine atoms). They also accumulate in the organic fraction of soil and in organisms.
The primary source of contamination of the atmosphere is ventilation of buildings with higher than ambient PCB concentrations. In the years 1955-1975, concrete-frame buildings are especially likely to have high levels of PCB contamination in the joint sealants. PCBs can be activated by mechanical working, so it is necessary, and in many countries a legal prescription, to verify the presence of PCBs before undertaking renovation or demolition work. This is often done in a joint inspection project by a specialist firm, checking for PCBs, CP, and asbestos in the one procedure. (See Case Study, Carbotech AG, Basel, Switzerland).
Air concentrations can reach 1 ng/m3 in city centres, and there have been cases of residential buildings having concentrations up to 35 ng/m3 in the USA.
PCBs biomagnify up the foodchain, with higher trophic level species having dangerous levels in aquatic environments, even if where the water is contaminated at even low concentrations. PCBs may also accumulate in aquifers. Birds can carry PCBs far from the water accumulation source, and deposit them through excretion and their bodies.
Human health concerns
PCBs are extremely toxic and a carcinogen. They are classifed as POPs (persistent organic pollutant). They are associated with endocrinal disruption, blocking the thyroid system function, and neurotoxicity.
People and animals are exposed to PCBs primarily through the ingestion of food, and to a lesser extent through skin contact and breathing in PCB-laden aerosols. Once in the body, depending on the type, PCBs may be excreted, converted to other chemicals, or retained by tissues and organs for years (the typical half-life of PCBs is 10-15 years). Since PCBs are easily absorbed by and retained by fat and milk, infants and people who lose weight suddenly can receive a toxic shock. Transplacental transfer to unborn babies is possible.
Three destruction techniques exist: chemical, thermal and biochemical. Each of these has limitations, high costs, and risk producing equally-hazardous secondary products
- The company Monsanto knew about the dangers of PCBs in the 1960s, but continued to manufacture them until 1972 without much restraint. In 2003, Monsanto was found guilty of negligence and suppression of the truth in a suit for damages in West Anniston, Alabama.
- 1968, Yusho disease resulting from the mixture of dioxins and PCBs in rice bran oil, debilitating thousands of people in Japan.
- High degree of contamination of soil by PCBs has been established at the US Okinawa Air Base, Japan.
- In Kenya, transformer oil was used as cooking oil. The oil was removed from transformers by thieves and passed to food vendors as cooking oil. The result was mass poisoning.
- By 1984, Brescia, Italy, had a PCB contamination crisis due to a Monsanto patent passing to an Italian company, whose manufacturing contaminated grazing land.
- Extensive PCB contamination occurred in the Soviet Bloc countries. For example, the Krupa River catchment was found in 1984 to have been severely contaminated by decades of unregulated PCB-containing wastes. Samples of soil, fish, water and domestic animals, today still contain high levels of contamination.
- 1999, Dioxin Affair in Belgium, in which animal feed was contaminated by PCBs, resulting in 9 million chickens and 60 thousand pigs being destroyed.
- Uncontrolled dumping of PCBs by Monsanto in Newport, South Wales, in a disused quarry continues to contaminate waste water discharges.
- Western Mediterranean cetacean species (dolphins and killer whales) have high blubber concentrations of PCBs, due to releases from Spanish sources.
- Landfills in many countries contain a legacy of dumped PCBs, mostly in transformers and capacitors, from where they may escape to the atmosphere or groundwater.
Regulations and Bans
Bans were imposed by countries, usually in two phases: for open (1970s) and later for closed applications (1990s-2000s). Equipment, such as electrical transformers and capacitors, could still be used, on the assumption their being sealed protected the environment. Leaks and poor disposal techniques eventually led to total bans on the manufacture and use of all PCBs.
The Stockholm Convention on Persistent Organic Pollutants (POPs) imposed a global ban on PCBs as of 22 May 2001, and listed them as one of the dirty dozen of known organic toxins.
In Germany, the EU PCB Directive has two emission values: Precautionary Limit (300 ng/m3 i ambient air) and Threshold Limit (3000 ng/m3 ambient air). Buildings with more than the Threshold Limit must be remediated immediately.
Dichlorodiphenyltrichloroethane (DDT) is an insecticide now banned in most countries, except in regions of Africa where it is considered the non-use would have consequences (malaria control) that would outweigh the risks of its continued use.
DDT was first used during the Second World War to combat insect-borne vectors of malaria and typhus. It was the subject of the 1962 book Silent Spring by Rachel Carson, which exposed the long-term impacts on human health and natural ecosystems of excessive and uncontrolled use of the compound in agriculture.
DDT is regulated by the Stockholm Convention on POPs (2001). In countries which have ratified Stockholm, DDT may only be used against insects which can cause disease, such as malaria.
Abstractive use is the use of water by which the water is temporarily lost as a resource.