Understanding of pesticides in waters and soils using a novel in situ
      dynamic sampling technique
Creators: name: Li, Yanying
Publisher: name: Lancaster University
Year: 2018

description: 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 (&lt;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.