Chemistry Reference
In-Depth Information
17
Organic Pollutants
Future Prospects
17.1 IntroductIon
During the second half of the 20th century, it was discovered that a number of organic
pollutants (OPs) were having harmful side effects in natural ecosystems, prominent
among which were chemicals that combined high toxicity (lethal or sublethal) with
marked biological persistence. Examples such as dieldrin, DDT, TBT, and methyl
mercury are represented in Part 2 of the present topic. Following these discover-
ies, restrictions and bans on the release of these chemicals into the environment
were introduced in many countries. Persistent organochlorine (OC) insecticides, for
example, were withdrawn from many uses and replaced by less persistent OP and
carbamate insecticides. More stringent legislation was brought in to control the pro-
duction and marketing of new chemicals, with clearer guidelines for environmental
risk assessment. Particularly strict rules were applied to new pesticides—something
of a double-edged weapon. This tightening of regulations has reduced the risk of new
pesticides creating new problems, but it may also have impeded the discovery and
registration of newer, more environmentally friendly compounds by making research
and development too expensive. In spite of the immediate advantages tighter regula-
tions bring, they can, in the long run, be counterproductive.
Since the introduction of these restrictions and bans on persistent pesticides, it has
been discovered that other less persistent compounds can also cause environmental
problems. Some highly toxic insecticides, including the carbamate aldicarb used as
a granular formulation, and the organophosphorous compounds carbophenothion
and chlorfenvinphos used as seed dressings, have been responsible for poisoning
incidents on agricultural land (Hardy 1990). Also, tributyl tin, an antifouling agent
used in marine paints, has been shown to have serious effects upon aquatic mollusks,
including oysters and dog whelks (Chapter 8, Section 8.3 of this topic). So, with the
tightening of the rules, other compounds of lesser persistence have been subject to
restrictions and bans. At the same time, some new pesticides have come on to the
market that are regarded as being more environmentally friendly. Among the insec-
ticides, newer pyrethroids and neonicotinoids fall into this category.
With these developments, it would appear that many of the more obvious envi-
ronmental problems relating to particular compounds or groups of compounds have
now disappeared. At least, this seems to be so in the developed world where there
are now strict controls of environmental pollution that are reasonably well enforced.
However, this does not necessarily apply to third-world countries where there is not
such strict control. One consequence of this trend in developed countries has been
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