ALL the way up at the North Pole, Arctic lakes are teeming with severe cases of pesticide contaminated fish. Dangerous levels of the pesticide toxaphene in the trout and turbot stock in Lake Laberge, in Yukon, Canada, have been reported by a team of Canadian researchers investigating the causes of pollution in surface seawater in the North Pole. This is in spite of the fact that toxaphene, a potentially toxic mixture of chlorinated camphenes, has been banned in Canada for over a decade. Scientists believe that the pesticides were carried from the tropics through air currents, to reach the erstwhile pure Arctic regions.
This spells bad news to the 200 native communities living around the lake. Since they consume large quantities of fish netted from these waterbodies, the locals are at serious risk, warns David Schindler of the University of Alberta, who led the study. "The more lakes we investigate, the more problems we find," he laments.
The research had begun 4 years ago, when a routine survey of fish in Lake Laberge found alarmingly high quantities of the pesticide. Now the study has revealed that contamination by toxaphene, dioxins and metals such as mercury, is much higher in the northern lakes of Canada than those down south. And, despite the banning of such toxic pesticides by most northern countries, the concentrations are still increasing.
The steady increase in the build up of these chemicals is mainly due to the widespread use of chemicals such as toxaphene in tropical Asia and Latin America, coupled with their high volatility, which causes them to vapourise easily from soils into the atmosphere, and the strong tendency of many of their compounds to persist in living organisms. According to Derek Muir, coauthor of the study, concentrations of toxaphene in turbot reached 2330 parts per billion in Lake Laberge. Toxaphene"s indirect impact on human beings is even more horrifying. It has been detected in the breast milk of women belonging to the Innuit community, which virtually lives on the fish they catch from Lake Laberge. The Canadian government has consequently been forced to ban all fishing activities for the time being.
The above scenario is the result of a "global distillation process", in which chemicals are vapourised from soils and transported on the winds to cold latitudes. There they condense out and become concentrated in the body fat of animals like fish, seals, polar bears and also humans. - from The New Scientist
Persistent organic compounds (poc), such as ddt and technical benzene hexa chloride (bhc), have not undergone any major reduction in their use, in spite of the fact that it has been banned in most Western countries. In India alone, 3,550 tonnes (t) of ddt and 31,600 t of technical bhc were produced in 1987.
ddt is widely used in tropical countries to control vector-borne diseases such as malaria and trypanosomiasis (sleeping sickness), while technical bhc is used as a cheap insecticide in agricultural production. Cyclodiens, such as aldrin and dieldrin are making their return for locust control, termite control and seed-dressing, mainly because of a lack of effective alternatives. The occurrence of pesticides containing polychlorinated biphenyls (pcbs) is related to increased industrial activity and the amounts used are increasing in the developing economies of Southeast Asia and South America, which are trying to retain their places in the global agricultural market. Their problem is to protect crops, at the same time keep their prices competitive. Moreover, agricultural output in many Western nations is subsidised by the government. The majority of the pests which threaten agricultural production are found in tropical areas. Many of the second and 3rd generation of pesticides are primarily designed for use in moderate climate ranges. Alternative pesticides of a non-persistent nature, such as organophopsphates, carbamates and pyrethroids can be costly, and push the products of developing countries out of the competitive global market. Upshod: the widespread use of cheap persistent pesticides.
Pesticide rotation programmes are required to control malaria vectors. These programmes use a variety of pesticides, including ddt, bhc, dieldrin, malathion, pirimiphos-methyl, bendiocarb and a variety of pyrethroids.
From a users point of view, pesticides such as ddt are ideal, because they are inexpensive and also have a low acute toxicity for mammals.
At present, developing countries are only holding 15 per cent of the global stock of pcbs. But because the presence of pcbs is related to industrialisation, the present rate of economic growth in many Asian and the South America countries will result in the developing countries" share going up soon.
A large proportion of pocs used in tropical countries are transported by air to the colder regions of the world. Some estimates of the contribution of aerial transport of technical bhc from tropical countries go up to as high as 99.9 per cent. The proportion of ddt volatilised during a 4-year period from an application on cowpeas in Nigeria, was an estimated 98 per cent.
Several models have been proposed to describe the processes involved in global transportation of pocs. According to one, organic compounds become fractionated as they reach higher latitudes, condensing at different ambient temperatures dependent on their volatility. A more comprehensive version of this model takes into account the distribution of persistent chemicals in a multi-phase system. In another model that was proposed, pesticides used in warm mid-latitude areas are transported in their gaseous state to the temperate regions, where they contribute to airborne fallout. In all models, aerial transport of pocs is thought to be a major factor in the global distribution of these components.
Over 8,400 tonnes of bhc residues are estimated to be present in the surface seawater of the North Pole. The trends in the temporal concentrations (that is, their presence over short periods of time) in the biosphere is not clear, and for some components an increasing trend is observed in the higher trophic levels, or, the levels of an ecosystem and its endemic food cycle.
A number of studies have tried to locate source-areas of high aerial concentrations of pocs in Arctic regions. Researchers observed and analysed the deposition of thousands of tonnes of brown particulate matter in northern Canada and found a variety of pocs, which they say have come from Asia. Over 10 per cent of the annual inflow of pocs to a number of lakes in the Arctic area was determined to have come from this Asian source.
It was found that in the Intuit community in northern Canada, 20 per cent of the individuals exceeded the acceptable daily intake (adi) for pcbs and ddt. Yet another study compares the concentrations of heptachlor group of pesticides (hch and hcb) used by farmers and ddt in the foliage of 26 different locations all over the world. The results indicate that concentrations of these compounds in the higher ranges of the Himalaya are among the highest in the world for hch isomers. Reported concentrations in foliage in the Himalayas are in an order of magnitude higher than those found in the circumpolar regions. The studies further demonstrated the importance of foliage in the bioaccumulation of pocs in the biosphere.
The bioconcentration factor (bf) of technical bhc from air to foliage is in the order of magnitude of 10 while the bf for ddt is established in the order of magnitude of 10. Comparable values for the bf for bhc using a compartment model for the uptake of pocs from air in foliage has been predicted.
pocs are evidently polluting the terrestrial and aquatic ecosystems and may threaten the existence of species not yet known to men. Oceans are sometimes thought to be permanent sinks of pocs. However, most organic carbon deposited in shallow marine environments are recycled by marine species. pocs are absorbed by phytoplankton. Accumulation of pocs in the food chain has resulted in high concentrations of the substances in a variety of predatory species which inhabit these ecosystems. Primary production in marine environment is significantly lower per unit of area than in terrestrial ecosystems, but biomagnification is generally higher in marine ecosystems as compared to terrestrial ecosystems. Although a certain proportion of the total annual input of pocs may reside for expanded periods of time in the hydrosphere (carried to deeper layers with downward currents at the colder parts of the ocean), a substantial part of the annual input is transferred back into the terrestrial biosphere as food for humans and animals. Further, the fraction of pocs transferred to the deeper layers of the ocean eventually resurface elsewhere and uptake in the marine food chain takes place.
Aerial transport of pocs from tropical areas to temperate and cold zones is a process which determines the global distribution of pocs. Although concentrations of pocs in food items, human blood, adipose (fat) tissues and breast milk in industrialised nations are generally substantially lower as compared to lesser developed countries, exposure to pocs in industrialised nations is sufficiently high to raise concerns about human health. It is clear that Western nations have a stake in the reduction of the use of pocs in lesser developed countries. (See Interview: David LaRoche, pg 53-54)
Global trade policy is a primary determinant for the use of cheap pesticides in agriculture. At first glance, the Global Agreement on Tariffs and Trade (gatt) may be helpful to reduce the use of cheap pesticides. It may, however, be expected that the financial gains as a result of the implementation of gatt will not be invested in the reduction of persistent pesticides, but to upgrade standards of living of farmers in lesser developed countries. Therefore, more effort should be invested to develop pesticides which are specifically meant for the climatic conditions in the developing countries. The majority of the 10,000 principal pest species and 600 weed species are found in the tropics.
The issue surrounding ddt and hch isomers is perceived as a problem in Western countries, while it often means survival in lesser developed countries. From this perspective, it is imperative that Western nations create economic incentives and supply financial and technical support to reduce the use of these components and (partially) foot the bill resulting from increase in the production costs of crops.
Measures to reduce the use of persistent pesticides for the control of vector-borne diseases (malaria, sleeping sickness) and for locust-control are more complicated. In 1985, dieldrin was reintroduced to control locusts in northern Africa. Other developments for locust control are more positive. A group of researchers in South Africa found that while applying pesticides to control locusts, natural enemies of the brown locust (Locustana pardalina) were encouraged by the application of low concentrations of deltamethrin.
Many research efforts have been dedicated to the development of a malaria vaccine. A variety of newly developed drugs are based on alkaloids isolated from indigenous plants, which have traditionally been used for malaria prevention. Among them, the sesquiterpene Yingzhaosu (artemisinine), from traditional Chinese medicine, and an extract from the roots of Cochlospermum angolense, used in the traditional medicine of Angola. Many new drugs look promising, but it may take a long time before these are sufficiently evaluated for potential side-effects. Further, resistance against drugs develops rapidly.
In conclusion, although progress has been made in the development of better medicines, malaria vaccines and therapeutic drugs to fight malaria and sleeping sickness infections, problems are mainly found in the implementation of the prevention programmes. These programs, in areas where sleeping sickness and malaria are endemic, rely on the use of cheap pesticides or other simple solutions, such as pesticide-impregnated bednets, until effective vaccines become available and are actually administered. Health effects associated with exposure to these pesticides are less severe than the disease for which they are intended, and less severe than the side-effects of some of the therapeutic drugs.
Evaluating this trade-off, the likelihood that cheap persistent pesticides will be used for an extended period of time to fight malaria mosquitos and tse-tse flies is great. The dynamics of locust-plagues resemble a disaster scenario, affecting the agricultural output of large areas. Inhabitants of target areas of swarming locusts will do everything possible to avoid crop loss. One of the more effective strategies is the use of large amounts of persistent pesticides. In the lesser developed countries, the presence of pcbs in the environment has not become a problem of the same magnitude as in many industrialised countries. There are, however, indications that the importance of pcbs in the environment is growing. Given the rapid industrial development of a number of countries in the mid-latitudes, technical support of the industrialised nations is necessary to minimise the use of pcbs in the process of industrialisation. This process will most likely result in the rise of production costs of goods. If the wealthy nations are serious about global reduction of pcbs, financial support to keep developing countries competitive on the global trade-markets may be required.
Research efforts to investigate the adverse effects on the environment and on human health should be much more concentrated in the areas where the components are actually used, and in some areas which have been under-researched so far. Studies can be conducted to establish the adverse effects of pocs on the general human population in developing countries. The adverse effects on infants should be monitored for an extended period of time. More detailed studies are necessary to establish occupational exposure and the associated health effects to workers with organochlorine pesticides and other persistent toxins.
Long-term studies are necessary to document the effects of extended exposure to humans. Although some studies have determined the presence of pocs in the different trophic levels of aquatic and terrestrial ecosystems, population studies are necessary to determine the effects on the composition and population dynamics of various ecosystems. The results of such studies may determine the urgency of the reduction of these components.
International efforts to reduce the production and use of compounds that threaten the quality of the global ecosystems have been moderately successful so far. The global reduction of chlorofluorocarbons (cfcs), as is being implemented under the Montreal Protocol to protect the ozone layer, can be implemented mainly because of the limited use of these compounds. Technology to replace these compounds is available, although more expensive. Western nations have demonstrated political will to reduce the output of carbon dioxide and sulphur dioxide, but progress to involve developing countries in these efforts is slow, and the overall progress is rather sluggish.
However, as compared to cfcs, carbon dioxide and sulphur dioxide, the prospects for rapid progress in reduction in use of pocs look rather bleak. pocs play a pivotal role to establish the basic requirements for existence in developing countries. Reduction of the use of these compounds calls for a dedicated and well orchestrated global effort in terms of research and international policy, if the entire earth is not to suffer from the adverse effects.
|Milk of human unkindness
Tabulated values for tDDT, tBHC & tPCB in human milk