Pesticide Degradation in Water - Pesticides: Evaluation of Environmental Pollution - page 118

Such polar pesticides tend to decompose into smaller molecules that have the potential
to be similarly or even more mobile, persistent, or toxic than their parent compounds.
Hence, their transport and behavior as well as biological activity may be different. In
general, the degradation products thus formed do not accumulate in soil. They are often
not effectively removed by water treatment processes (e.g., activated carbon) and even
new toxic degradation products are formed when chlorination or chloramination is
employed.
Such products of biological and chemical transformation have been detected
in all environmental compartments, including groundwater and surface waters.
Several cases have been reported where single transformation products are present
in higher concentrations or detected more frequently than their parent compounds.
Important examples include pesticides such as organochlorine compounds, triazines,
or chloroacetanilides.
The discovery of the occurrence of degradation products in drinking water provides
important insight into how our vision of surface water and groundwater contamination by
pesticides is limited when the only samples of parent compounds are analyzed. Therefore,
there is a need to understand better the impact of degradation products on the environ-
ment and to have knowledge of the occurrence and significance of pesticide residues in
water. Detection of transformation products will spur investigation of pesticide degrada-
tion pathways in an aquatic environment to identify other possible toxic transformation
products.
In the past, such polar metabolites could hardly be detected with available analytical
methods. The lack of suitable instrumentation was a handicap for the detection of these
degradation products in the environment when the market launched these polar pesti-
cides. Nowadays, development of analytical strategies is essential for monitoring these
very polar transformation products in natural waters and, consequently, for understand-
ing the fate of the parent compounds in the environment. As monitoring efforts have
increased and analytical methods have become more sensitive, there have been many
more detections of pesticides in water and more public concern about the possible health
effects of these residues. In this sense, development of new analytical methods is needed
to determine trace concentrations of very polar pesticide analytes.
Concerns will increase further if it turns out that some of the environmental degrada-
tion products of the pesticides have toxicological effects. Yet, for many of the currently
used pesticides, the fate and significance of their degradation products in the aquatic
environment are not clearly understood and therefore, continuous research is still
needed. Studies should be aimed at the identification of major degradation pathways
and mechanisms of degradation of pesticides and identification of new degradation
products and their behavior in the environment. The determination of their physico-
chemical properties would also be desirable in order to know their persistence and
mobility in the environment. In addition, the study of their toxicity, the development of
long-term studies to determine the effects of persistent substances, and studies about
interactions with their parent compounds and with other degradates and their effects
on soil and microorganisms will be helpful to know their significance and impact in the
environment. To achieve this task, predictive approaches such as QSARs or QSPRs may
be employed.
These studies could lead researchers to consider including selected degradation prod-
ucts in environmental monitoring programs and to a better enforcement of legislation. All
these issues are formidable challenges that environmental chemists will have to face in the
forthcoming years.