Organophosphorus and Carbamate Insecticides - Organic Pollutants: An Ecotoxicological Perspective - page 202

tissue levels of insecticide. Consequently, the development of this type of resistance
may increase the risk of secondary poisoning of insectivores by OPs. Thus, a number
of different routes of transfer need to be taken into account when considering the fate
of OP insecticides applied on agricultural land.
BOX 10.1 ORGanOpHOSpHORuS “neRve GaSeS”
Chemical warfare agents, such as soman and sarin, sometimes termed nerve
gases , are powerful anticholinesterases, which bear some resemblance in
structure and properties, to the OP insecticides. A major difference from most
insecticides is their high volatility. These agents were possessed by the major
powers during World War II, although they were never employed in warfare.
More recently, with the end of the Cold War, there has been a reduction in
their stockpiles, in keeping with arms reduction treaties. At the same time, it
has come to light that badly disposed canisters containing chemical weapons
and originating from World War II are still around, for example, in some areas
of the Baltic Sea. Thus, questions have been asked about their possible impor-
tance as environmental pollutants.
There continues to be public concern about the possibility of their being
used in future. When Saddam Hussein was in power in Iraq, there was evi-
dence that a chemical weapon of this type was used against Kurdish villag-
ers. Subsequently, it was widely believed that these were among the weapons
of mass destruction held by Saddam Hussein's regime; weapons that failed to
materialize after the invasion of Iraq in 2003. Since these events, there has been
concern that weapons of this type may be in the possession of “rogue” states—
or individual terror groups.
There have been suspected cases of human exposure to these compounds.
One issue has been the possible exposure of soldiers to them during the Gulf
War of 1991. Some have suggested that this may have contributed to what has
been termed the Gulf War syndrome , a condition reported in some NATO
soldiers serving in the Gulf War. Also, during the post-Cold War era, there
has been discussion about the safe disposal of the large stockpiles of chemical
weapons held by the major powers (see also Chapter 1).
10.2.4 T o x i c i T y
The primary site of action of OPs is AChE, with which they interact as suicide sub-
strates (see also Section 10.2.2 and Chapter 2, Figure 2.9). Similar to other B-type
esterases, AChE has a reactive serine residue located at its active site, and the ser-
ine hydroxyl is phosphorylated by organophosphates. Phosphorylation causes loss of
AChE activity and, at best, the phosphorylated enzyme reactivates only slowly. The
rate of reactivation of the phosphorylated enzyme depends on the nature of the X
groups, being relatively rapid with methoxy groups (t 50 1-2 h), but slower with larger