Understanding of pesticides in waters and soils using a novel in situ dynamic sampling technique

Li, Yanying (2018) Understanding of pesticides in waters and soils using a novel in situ dynamic sampling technique. PhD thesis, UNSPECIFIED.

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There has been increasing concern about the widespread occurrence and persistence of pesticides in the environment. Pesticides can transport among and between environmental compartments, causing pollution in water, soil and air, and posing potential risks to humans and the ecosystem. There is a need to study the fate and behaviour of pesticides in the environment. Over the last few decades passive sampling approaches have aroused attention in detecting pesticides, but they are still under development. In this thesis, the passive sampling technique of diffusive gradients in thin-films (DGT) was developed and validated for pesticides in water and soils for the first time. The DGT technique was developed for in situ measurement of 9 pesticides in water. The compounds were carefully selected to represent a wide range of properties and classes, so that the technique may have wider applicability in future. Two types of binding material (HLB and XAD 18) were used and compared. Laboratory testing was carried out with various controlled experiments. HLB showed higher binding capacity but with slower uptake than XAD 18. The principle of DGT was confirmed as the mass accumulated by DGT was inversely related to the thickness of diffusive layer and proportional to the deployment time. The performance of the DGT sampler was found to be independent of pH (4.7-8.2), dissolved organic matter concentration (<20 mg L-1) and ionic strength (0.01-0.25M). Several laboratory and field trials were conducted to confirm the usage of DGT for in situ measurement of pesticides in water and soils. DGT has great potential to be applied to trace organic contaminant studies in soils and sediments, but so far work research on this line has been very limited. DGT was therefore investigated for in situ measurement of atrazine (ATR) and its 5 metabolites in soils, and compared with other two approaches to predict bioavailability to maize and to assess the ATR degradation pathway. The results showed that DGT performed best in measuring the bioavailability of total ATR (ATR and its metabolites) to maize. Hydroxylation was the dominant degradation procedure during aging and maize growth in the test soils. This could be well characterized using DGT. DGT was also deployed in a group of aged soils with different pH, soil types and ATR contaminated levels, to explore the behaviour of atrazine in soils and its sorption/desorption. Soil properties had influence on the labile pool size (Kd) and re-supply capability of ATR (R), while aging affected the labile pool in some soils, but had only a slight influence on re-supply. The DIFS (DGT-induced fluxes in soil/ sediment) model was employed to further characterize the kinetics of desorption from the solid phase to the solution phase, this showed that desorption kinetics and the labile pool size commonly affected the re-supply. Owing to the frequently simultaneous occurrence of ATR and arsenic (As) in the environment, DGT equipped with precipitated ferrihydrite binding gel was deployed to investigate the effect of ATR on the availability of As in soils. The addition of ATR did not impact on the measurements of As availability in the test soils, in the concentration range (up to 50 mg kg-1 ) used. This research has demonstrated that DGT is an effective tool for measuring pesticides in soils and waters. It can be used for monitoring purposes, and in experiments designed to better understand pesticide fate, behaviour, availability and to help with assessment of their risk in the environment.

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Thesis (PhD)
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30 May 2018 15:40
Last Modified:
18 Sep 2023 02:19