Pesticides: Valuable poisons when kept under control

By Ian Shaw and Janahar Murad

JAKARTA (JP): Insect pests eat the food that farmers produce to satisfy our hunger, but the pesticides used to kill them may have a harmful effect upon consumers and exert long-term effects upon the environment.

The European Union, U.S., Australia and New Zealand are among those dealing with the problem by employing strict legislation governing both the use of pesticides by farmers and the control of pesticide residues in food. Such legislation is far-reaching and has an impact upon imported food, which must also comply with the nations' statutory requirements for residues.

A pesticide either remains on the surface of, or is absorbed into, the plant or animal. After application, most pesticides degrade, either spontaneously or aided by the host's metabolic system. As time passes, levels of pesticide in the animal or plant diminishes, until eventually most modern pesticides disappear altogether within a few weeks.

Some of the older pesticides, for example DDT, can reside in the hosts for entire life spans. DDT is an organochlorine pesticide, most of which are banned or heavily restricted because of their extremely long residence time in living organisms and the environment. DDT is incredibly persistent -- it is thought to take more than 50 years for its level to decrease by 50 percent -- and it is likely that every cell in every living plant and animal on earth harbors at least one DDT molecule, or its metabolite, DDE. They have been found in the remotest parts of the world, including Antarctica, where they were never used.

In 1962, Rachel Carson's Silent Spring brought to the world's attention to the potential devastation of overuse of pesticides. She predicted the large scale death of birds, hence her book's title, due to food being contaminated with pesticide residues. Fortunately, she exaggerated terribly and her predictions have not come true. Despite her overstatement, the world listened and acted, and it could be said that her writings averted a global disaster.

Now, however, some of the sinister long-term effects of pesticides are beginning to manifest on a global scale. Insects are developing resistance to many insecticides, and plants to herbicides. Farmers need to use more of the pesticide to get the same effect, or mix pesticides, which might be more harmful in the long term.

In rich countries, new pesticides are developed both to combat resistance and increase the income of their manufacturers. Such new pesticides must comply with strict approval requirements, which means effects upon people and the environment are likely to be minimal.

In poor countries, however, there is less pressure to develop replacements, possibly because modern pesticides are expensive. Thus, the amount of pesticides used increases, along with the environmental harm they cause as residues in food increase.

A more recent and disturbing impact of manmade chemicals upon the environment involves the chemical mimicking the sex hormones. They fool cells in the animal into thinking a sex hormone is present. For example, DDT resembles the female sex hormone estradiol. It causes animals to express the characteristics switched on by the hormone; if a male animal is exposed to estrogen-mimicking chemicals, it develops female characteristics.

This might sound far-fetched, but there is evidence of its occurrence. Male alligators in Florida have smaller penises than 20 years ago, trout in English rivers are beginning to manufacture female egg proteins and the human sperm count is plummeting. These changes are caused by several groups of chemicals, the most important being plasticizers, but pesticides undoubtedly contribute to the effect.

It is important to monitor the food chain for pesticide residues to keep a check on the average total consumption of pesticides in the diet. In the U.K., this is managed by the government's Working Party on Pesticide Residues (WPPR). They analyze about 3,000 samples of meat, fruit and vegetables each year, and produce an annual report. This is used by government to assess risks to the consumer and by the public who are becoming increasingly concerned about the food that they eat.

The WPPR's work is reassuring because it shows that most food contains little or no pesticide residues. In 1996, less than 1 percent of food monitored contained residues above the statutory limit, but 34 percent contained traces of pesticides. This monitoring program is not only important in checking the food chain, but also allows penalties -- warnings and fines -- to be applied to farmers contravening the pesticide usage regulations.

Indonesia has an excellent pesticide regulatory system, run by the Ministry of Agriculture and implemented by the Pesticides Committee. Its pesticides' approvals scheme is very similar to that operated in the U.K.

Before a pesticide is licensed for use, an assessment of its toxicity to both people and the environment is made. If the risk of using it is outweighed by its benefit (e.g. in terms of food production) then it will be passed for use. In order to be certain that this system is working it is essential to operate a monitoring program. Such a program guards against illegal use and harvest or culling before the appropriate withdrawal time (i.e. the time between application of a pesticide and harvest).

The country is developing a monitoring program, but currently samples only a small number of foods for analysis, primarily because of the high cost (the U.K. monitoring program costs 2M per year to run, a figure which does not include the set-up costs). Last year, Indonesia analyzed 40 fruit and vegetable samples as part of its pesticides program.

Seventeen samples contained pesticide residues (this figure might include samples with multiple residues), and only one sample was at the international statutory limit. No DDT was reported. This is better than in 1991, when DDT was present in 28 of the 133 residues from 143 samples.

It is important the development of monitoring programs continues. This is primarily to protect the consumer from potentially harmful levels of pesticides in their food, but also to allow the government to monitor progress in the use of pesticides in the country and minimize harm to the environment.

The time is right to review the use of pesticides throughout the world so that we can prevent Rachel Carson's worst predictions coming true. Her fears were related to the short-term effects of pesticides, but we are today becoming aware of the rather more sinister long-term effects. Unless checked, these could affect plants and animals so slowly that the changes would be difficult to detect until it was too late.

Prof. Ian Shaw is head of the Center for Toxicology in the University of Central Lancashire, Preston, U.K. and chairman of the WPPR. He is a frequent visitor to Indonesia where he is developing a British Council-funded environmental toxicology and collaborating with Janahar Murad, a researcher at the National Institute of Health Research and Development and a member of the Indonesian Pesticide Committee.