Pesticide Residues in Surface Water and Groundwater - Pesticides: Evaluation of Environmental Pollution - page 276

treatment by ozone is very effective because it yields very high degradation of pesticides
and induces far less toxic products than chlorination. The combination of activated carbon
adsorption and ozonization was found to be the most efficient method for degrading the
majority of pesticides in the water purification process (Ormad et al. 2008).
9.5 Methods for Monitoring Pesticide Residues in Water
For the protection of human health and the environment, pesticide residues are routinely
monitored in food, water, soil, and tissue samples. The survey on pesticide residues in the
environment is faced with the identification and quantification of hundreds of compounds
with widely different physicochemical properties. Furthermore, ultrasensitive analytical
methods are mandatory since the water tolerable limits for most of the pesticides are in
low levels of μg/L and, in some cases, ng/L (Council of the European Union 1998, 2008). To
be detectable and quantified, the substances present in trace levels must be extracted and
concentrated prior to chemical analysis.
Pesticide residues are isolated and concentrated from water samples using different
extraction procedures, such as liquid-liquid extraction (LLE) or solid-phase extraction
(SPE), usually followed by a solvent evaporation step (Gan and Bondarenko 2008). Gas
chromatography (GC) or liquid chromatography (LC) coupled with conventional detec-
tors, such as flame ionization detector (FID) (Pico et al. 1994), electron capture detector
(ECD) (Lipinski 2000), nitrogen-phosphorus detector (NPD) (Lipinski 2000), ultraviolet-
visible (UV/VIS) (Chiron et al. 1995; Curini et al. 2001), photodiode array (PDA) (Carabias-
Martínez et al. 2005), or fluorescence detector (FLD) (Chiron et al. 1995), has been
traditionally applied for pesticide residue analysis. Currently, the determination of pes-
ticide residues requires the use of the chromatographic techniques hyphenated to mass
spectrometry (MS) as the detection system. In general, MS is widely applied in trace
analysis due to its selectivity, sensitivity, and confirmation capability (Gonçalves and
Alpendurada 2004).
Different strategies could be applied for monitoring pesticides in water, depending
on the objectives pursued (target or nontarget analysis). Both types of analysis have
the need for different analytical schemes and may require different instrumentation.
An example of target analysis is the inspection of pesticide EQS in surface water. The
relevant analytes are preselected by the residue definition given in the EQS regulation
(Council of the European Union 2008). In contrast, the EU regulation on residues in
drinking water does not contain detailed residue definitions (Council of the European
Union 1998). Besides, monitoring and identifying pesticide degradation products, which
is considered to be crucial for complete environmental risk assessment, also requires a
nontarget analysis. For nontarget screening, instruments must be able to generate suf-
ficient information for the elucidation of residues, such as accurate mass, from which
empirical formulae can be deduced.
9.5.1 Sample Preparation
Due to the low levels of pesticides detected in the environment and the complexity of the
environmental matrices, preconcentration and cleanup of the samples, prior to chemical
analysis, is usually required. The preconcentration is achieved through phase transfer,