Environmental Engineering Reference
In-Depth Information
reported in the literature for the trace enrichment of transformation products of pesti-
cides from water are alkyl-bonded silicas, especially C-18 (Hernández et al. 2001; Huang
et al. 2003; Steinheimer 1993), and copolymer sorbents such as cross-linked polystyrene
divinylbenzene (D'Archivio et al. 2007; Gervais et al. 2008; Picó et al. 2007; Sandín-España
et al. 2002). However, other sorbents are also applied for polar pesticides, obtaining good
recoveries. Cai and coworkers (1995) determine trace levels of didealkylatrazine (DDA),
one of the dealkylated products of atrazine degradation with graphitized carbon black
cartridges, with recoveries greater than 80%. These recoveries were one order of mag-
nitude greater than those achieved with C-18 bonded silica cartridges due to the higher
polarity of DDA than atrazine. Santos and coworkers (2000) developed a method for the
trace determination of acidic and neutral herbicides (bentazone, 2,4-D, propanil, (4-chloro-
2-methylphenoxy)acetic acid (MCPA), 4-(4-chloro-2-methylphenoxy)butanoic acid (MCPB),
molinate) and some of their transformation products (8-hydroxybentazone, 6-hydroxyben-
tazone, 2,4-dichlorophenol, 3,4-dichlorophenol, and 4-chloro-2-methylphenol). Due to the
wide range of polarities of the studied compounds (log K ow ranged from 1.26 to 5.84), the
stationary phase selected for the extraction of the analytes was the styrene-divinylbenzene
copolymer, PLRP-S. Recoveries for the analytes were higher than 76%.
The drawback of these sorbents is the limited selectivity. In addition to the analytes,
many water constituents such as HAs and FAs are enriched in the sorbent and interfere
in the chromatographic separation. This occurs especially in the case of transformation
products (Chiron et al. 1993; Hennion 1991; Hogendoorn et al. 1999) where the matrix peak
coeluted with these compounds which are generally more polar than the active substance.
The increase in selectivity has been obtained by the development of molecularly
imprinted polymer materials. These sorbents are extensively cross-linked polymers
containing specific recognition with a predetermined selectivity for analytes of interest
(Bjarni Bjarnason et al. 1999; Hogendoorn and Zoonen 2000; Koeber et al. 2001). The pre-
concentration of the target compound and the simultaneous elimination of sample matrix
interferences result both in an excellent chromatographic resolution and in an increase
in sensitivity of the analysis (Rodríguez-Mozaz et al. 2007). However, few MIPS sorbents
have already been developed for the analysis of the transformation products of the pesti-
cides. Carabias-Martínez and coworkers (2005) obtained a molecularly imprinted polymer
obtained by precipitation using propazine as template for the determination of triazine
herbicides and some of their hydroxylated and dealkylated metabolites from river water.
The LODs obtained were lower than 0.1 mg/L, the limit established by EU legislation as
the maximum concentration allowed for individual pesticide residue in drinking water
(European Commission 1998).
4.7 Future Trends
Nowadays, the number of existing active substances currently employed as pesticides is
quite large, belonging to different families such as organophosphate, pyrethroid, and neo-
nicotinoid insecticides; phenoxy, dinitroaniline, and sulfonylurea herbicides; and dithio-
carbamate and strobulirin fungicides.
Over the last few years, the production and application of pesticides have changed.
Polar and more easily degradable pesticides have replaced nonpolar and persistent ones
in order to decrease environmental persistence and reduce nontarget organism toxicity.
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