Pesticide degradation and export losses at the catchment scale: Insights from compound-specific isotope analysis (CSIA)

Abstract

Although pesticides undergo degradation tests prior to use, determining their export, degradation and persistence under field conditions remains a challenge for water resource management. Compound specific isotope analysis (CSIA) can provide evidence of contaminant degradation extent, as it is generally independent of non-destructive dissipation (e.g., dilution, sorption, volatilization) regulating environmental concentrations. While this approach has been successfully implemented in subsurface environments, its application to pesticides in near-surface hydrological contexts at catchment scale is lacking. This study demonstrates the applicability of CSIA to track pesticide degradation and export at catchment scale and identify pesticide source areas contributing to changes in stable isotope signature in stream discharge under dynamic hydrological contexts. Based on maximum shifts in carbon stable isotope signatures (ΔδC = 4.6 ± 0.5‰) of S-metolachlor (S-met), a widely used herbicide, we estimate maximum degradation to have reached 96 ± 3% two months after first application. Maximum shifts in nitrogen isotope signatures were small and inverse (ΔδN=-1.3±0.6‰) indicating potential secondary isotope effects during degradation. In combination with a mass balance approach including S-met main degradation products, total catchment non-destructive dissipation was estimated to have reached 8 ± 7% of the applied product. Our results show that CSIA can be applied to evaluate natural attenuation of pesticides at catchment scale. By providing a more detailed account of pesticide dissipation and persistence under field conditions we anticipate the contribution of pesticide CSIA to the improvement of regulatory and monitoring strategies.

Carbon and nitrogen stable isotope fractionation during abiotic hydrolysis of pesticides

“…In comparison, ε C values have been obtained for biotic degradation of S-Metolachlor (ε C z 0‰, degradation 30%), Alachlor (ε C ¼ À2.0 ± 0.3‰, degradation 60%) and Acetochlor (ε C ¼ À3.4 ± 0.5‰, degradation 65%) in a constructed wetland (Elsayed et al, 2014) or for S-Metolachlor biotic degradation (ε C ¼ À1.5 ± 0.5‰, degradation ! 80%) in soil incubation experiments (Alvarez-Zaldívar et al, 2018). Small differences in isotopic fractionation during chloroacetanilide hydrolysis and biotic degradation may reflect distinct mechanisms, which is supported by the formation of different degradation products.…”

“…Among anilide pesticides, S-Metolachlor, Acetochlor and Alachlor are the most applied herbicides worldwide (Atwood and Paisley-Jones, 2017), Butachlor is commonly used in Indian rice fields (Armanpour and Bing, 2015), while Metalaxyl is a common fungicide in European vineyards (Kom arek et al, 2010). Anilide pesticides are mainly made of carbon (z 60%, Table 1) and change in d 13 C values have been used to evaluate chloroacetanilide degradation (Elsayed et al, 2014;Alvarez-Zaldívar et al, 2018). In the case of chiral pesticides, such as Metalaxyl, CSIA and enantioselective analysis can be combined for Enantio-specific Stable Isotope Analysis (ESIA) to evaluate separately the isotope composition of each enantiomer (Badea and Danet, 2015;Masbou et al, 2018).…”

“…Because substantial biodegradation can occur without significant deviations of the enantiomeric fractions (EFs), ESIA has become a promising new approach that can provide insight into enantioselective fates and source apportionment of environmental organic contaminants (Badea and Danet, 2015). Although high detection limits of isotope ratio mass spectrometry and small contribution of nitrogen (i.e., only one N heteroatom in the chloroacetanilides) challenge multi-element CSIA of anilide pesticides at environmental concentrations (Lutz et al, 2017), sample preconcentration (>1000 times) recently allowed dual N and C-CSIA of S-Metolachlor at an agricultural catchment (Alvarez-Zaldívar et al, 2018). However, reference C and N isotopic fractionation ε for transformation reactions involving anilides are lacking so far.…”

Solid-phase extraction method for stable isotope analysis of pesticides from large volume environmental water samples

“…16 Various analytical methods have been recently developed. [17][18][19][20][21][22][23][24][25][26][27][28][29] Nonetheless, application of CSIA of pesticides to field studies remain scarce 24,[30][31][32][33][34] because of two major challenges. First, isotope effect-free extraction and pre-concentration methods are required to allow CSIA at low environmentally relevant concentrations by gas chromatography-isotope ratio mass spectrometry (GC/IRMS) or -in the case of compounds like desphenylchloridazon for which GC/IRMS-based carbon isotope analysis does not work -by liquid chromatography-IRMS (LC/IRMS).…”

Evaluation of azamethiphos and dimethoate degradation using chlorine dioxide during water treatment

“…Anthropogenic activities, e.g., industrial and agricultural activities, mining, and climate change induced by these activities, can influence and change groundwater flows and also influence water quality by introducing contaminants (Milojković et al 2018;Azizian et al 2017;Şener et al 2017). Water quality is clearly important for both human and aquatic life (Adityosulindroa et al 2018;Matsushita et al 2018;Alvarez-Zaldívar et al 2018).…”