Twenty-eight chemicals that cause health problems including cancer and reproductive disorders – and sometimes death – are banned or restricted under the Stockholm Convention, one of the most critical international agreements administered by UN Environment.
Known as persistent organic pollutants, or POPs, industry and agriculture has released these toxins over decades, and they have spread far and wide, even to the Arctic. They remain intact for years in the environment and “bio-accumulate” in organisms higher up the food web, including large fish and predators. They poison both people and wildlife.
Their effects also include allergies and hypersensitivity, damage to the nervous systems and disruption of the immune system. Some POPs are considered endocrine disrupters: by altering the hormonal system, they can damage the reproductive and immune systems of people and their children.
In force since 2004, the Stockholm Convention is central to global efforts to protect human health and the environment. Combating pollution is the focus of the UN Environment Assembly to be held in Nairobi in December.
Here are some of the dangerous substances covered by the convention.
Dichlorodiphenyltrichloroethane (DDT)
The discovery of dichlorodiphenyltrichloroethane’s effectiveness against insects won Swiss chemist Paul Müller a Nobel prize in 1938. For years, it was used with great results against malaria-carrying mosquitoes, typhus-transmitting lice and on farmers’ fields the world over. But, as with other blockbuster pesticides, DDT was too good to be true. Rising concern about its impact on wildlife (it thinned the eggshells of iconic birds including the bald eagle and peregrine falcon) and humans made it a prime target of the emerging environmentalist movement in the 1960s. Identified also as a potential human carcinogen, the US outlawed the use of DDT in agriculture in 1972 and other countries followed suit until the convention extended the ban worldwide. Some exemptions are still allowed for fighting malaria.
Polychlorinated biphenyls (PCBs)
Though banned in some countries as early as the 1970s, the amount and persistence in the environment of polychlorinated biphenyls is so great that these industrial chemicals remain a worry nearly a half-century later. Prized for their stability, they found a wide array of uses including as coolants, hydraulic fluids and lubricants, and as additives in paint, paper and plastics. Large numbers of people have been exposed to them through food contamination. PCB-laced rice oil poisoned thousands of people in Japan in 1968 and in Taiwan in 1979. Symptoms included pigmentation of nails and mucous membranes and swelling of the eyelids, along with fatigue, nausea, and vomiting. In North America, studies showed that children of mothers who ate large amounts of contaminated fish from Lake Michigan had poorer short-term memory function.
Hexochlorobenzene (HCB)
Introduced in 1945, hexochlorobenzene is a fungicide that was widely used on wheat and other crops. But when people in eastern Türkiye ate bread made with treated seed grain in the 1950s, thousands of them fell ill and hundreds died. Many were affected by a liver condition that resulted in skin lesions. Breastfeeding children whose mothers had eaten tainted bread died while suffering from a condition known as “pink sore”. Decades later, researchers found that HCB levels in the breast milk of affected women was still elevated. The chemical causes cancer as well as reproductive failure in animals and is therefore considered a possible carcinogen for humans. It has been found in food of all types. One study of Spanish meat found it in all samples.
Hexachlorocyclohexane
Hexachlorocycohexane and related pesticides including Lindane are among the many POPs that have accumulated in the Arctic, many thousands of kilometres from where they were produced. Currents in the atmosphere and the oceans as well as food webs topped by species including seals and whales have deposited them there over decades. Now climate change is causing the release of these toxins from ice, snow and frozen soils, where they have been trapped since the last century. This story could have a worrying epilogue for the Arctic’s indigenous peoples. Their diets typically include large amounts of fish and wild foods that are high in fat – exactly where concentrations of these dangerous compounds are highest.
Hexabromocyclododecane (HBCD)
Hexabromocyclododecane, or HBCD, is a relatively recent concern, and one of 16 chemicals added to the convention since it came into force. Like several others, it has been prized mainly as a flame retardant. Since the 1980s, it has been added to polystyrene foam insulation boards used in construction. It has also been used on textiles, including tatami mats and bean bags, and in electrical equipment such as fridges. Releases of HBCD to the environment – during manufacturing, use and disposal – were still increasing a few years ago and a lot of it is still out there in buildings. Significant levels of HBCD in human milk and exposure through food has been reported near local sources. The main risks are possible neuroendocrine and developmental disturbances, especially in young children. It is considered very toxic to aquatic organisms and studies suggest it could severely affect neuroendocrine systems in mammals. Researchers have found high concentrations in terns and falcons around the British Isles, in mandarin fish and grass carp in China’s Yangtze River, and in Svalbard’s polar bears.
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