Pesticide Degradation in Water - Pesticides: Evaluation of Environmental Pollution - page 114

environment are not known and no data exist on their physicochemical properties, envi-
ronmental fate, and toxicity; and (d) Among the numerous metabolites and degradation
products detected in laboratory experiments, which are the most likely to be monitored?
There is no information about which of them will be significant in the environment, that
is, to occur in surface waters and groundwater and/or have biological activity.
Although GC has been used to determine pesticides and their transformation products,
liquid chromatography (LC) is found to be more adequate as the majority of the transfor-
mation products are more polar than their parent pesticides, less volatile, and often also
thermolabile. Undoubtedly, MS is one of the best techniques for the elucidation of transfor-
mation products due to its sensitivity, universality, and the sample information provided.
LC-MS has permitted to achieve the restricted levels required by the European Directive
(Alder et al. 2006; European Commission 1998).
One of the main problems in developing multiresidue methods is due to not only the
wide range of polarities that present the great variety of pesticides but also the analysis of
transformation products that are generally more polar than the parent pesticides.
Quadrupole mass analyzers have been frequently employed in the analysis of pesticide
residues in water (Sandín-España et al. 2005). However, the main drawback is the lack of
accuracy for the determination of pesticides and their degradation products in a complex
matrix with interferences that coelute. Triple quadrupole mass analyzer is, nowadays, one
of the most widely used techniques for the routine analysis of pesticides in the environ-
ment (El Atrache et al. 2005; Hernández et al. 2004; Lehotay et al. 2005; Marín et al. 2009;
Rodrigues et al. 2007). This technique is highly selective and sensitive but it does not per-
mit structural elucidation of nontarget compounds (Bobeldijk et al. 2001).
The development of hybrid quadrupole time-of-flight (QTOF) instruments repre-
sents an attractive new tool for the determination of transformation products in the
environment (Ferrer et al. 2004; Meng et al. 2010). The high resolution and accurate
mass measurements provided by the TOF analyzer allow for the assignment of a highly
probable empirical formula for each compound, the differentiation between nominal
isobaric compounds, and the possibility of performing MS/MS spectra with accurate
mass measurement of the identification of the transformation products (Grimalt et al.
2010; Keizer et al. 2001). Thus, QTOF analyzer is a great advantage in the elucidation of
unknown compounds. In addition, it permits the possibility of obtaining the elemental
compositions of all of the product ions obtained, which is very helpful to elucidate the
transformation products in the environment (Barceló and Petrovic 2007; Bobeldijk et al.
2001; Brix et al. 2009; Trovó et al. 2009).
The increase in polarity makes the isolation and analysis of transformation prod-
ucts more difficult than the analysis of the parent compounds. Thus, the analysis of
pesticide degradation products almost begins with the problem of the isolation of
metabolites from the water sample (Bagheri et al. 1993; Guenu and Hennion 1996;
Sandín-España et al. 2002).
Following isolation of the degradation products, the compounds are identified usually
by a chromatographic method. This identification is sometimes hampered due to the lack
of the analytical standard available. Therefore, the synthesis may be required. The effort
and cost are sometimes great, and this fact has discouraged studies of transformation
products in groundwater and surface waters. For these reasons, the analysis of pesticide
transformation products has not proceeded as quickly as the detection of the parent com-
pounds. In addition, knowing which of the degradation products of a pesticide may be
important in surface waters and groundwater is a difficult question and requires different
types of understanding, such as transport, persistence, and toxicity.