Pesticides: Valuable poisons when kept under control

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.