Development and applications of the diffusive gradients in thin-films (DGT) technique for the measurement of polycyclic aromatic hydrocarbons (PAHs) in waters and soils
Creators: name: Rong, Qiuyu
Publisher: name: Lancaster University
Year: 2024

description: Polyaromatic hydrocarbons (PAHs) are a group of organic compounds, widely
 present in the environment, which are carcinogenic, teratogenic, mutagenic
 and bioaccumulative. They can exist in the environment for a long time and
 pose potential risks to humans and ecosystems, so they have attracted the
 attention of research scientists and regulators. It is therefore important
 to have sampling and analytical techniques to accurately and effectively
 detect PAHs, to understand their environmental sources, behaviour and
 fate, to provide a scientific basis for controlling their releases to the
 environment and to protect ecosystem and human health. 
 
 
 The diffusive gradients in thin films (DGT) technique is an in-situ
 passive sampling technology, which has been used to measure heavy metals,
 nutrients and – more recently – some classes of organic pollutants in
 environmental media. In this thesis, a DGT sampler for PAHs was developed,
 tested, and used for studies of PAHs in waters and soils. A new sampler
 casing was designed using
 
 aluminum, to reduce adsorption during field deployment. The performance of
 three binding materials (MIP, HLB and XAD18) was compared in laboratory
 tests. The absorption capacity and uptake kinetics of the three materials
 were determined, and their performance under different pH, ionic strength
 and dissolved organic matter tested. The MIP-DGT sampler performed best
 and
 
 was not affected by environmental conditions across the range pH
 (3.9-8.1), ionic strength (0.01- 0.5 M) and dissolved organic matter
 concentration (&lt;20 mg L
 
 -1 ). Field tests showed DGT can be used for time-integrated in situ
 measurement of PAHs in waters under a range of environmental conditions.
 
 
 DGT PAH samplers were deployed in the Nanjing section of the Yangtze River
 and urban rivers in summer and winter 2021. The concentrations of labile
 PAHs had marked seasonal differences under the influence of source inputs,
 river flow differences, and degradation/loss processes. The accumulation
 of PAHs in the Yangtze River upstream of Nanjing together with seasonal
 combustion sources, discharges from petrochemical enterprises and ship
 transportation are
 
 discussed as the main sources of PAHs in the studied area. Inputs from
 Nanjing urban rivers had little impact on the PAH mass loadings in the
 mainstream of the Yangtze River. The results of two different risk
 assessment methods showed that PAH concentrations are sufficient to be a
 potential risk to ecological systems during the winter and in some of the
 more contaminated industrial areas.
 
 This study highlighted how in situ DGT water sampling can be used to
 investigate the sources, fates and behavior of PAHs in aquatic
 environments.
 
 
 DGT can also be used to study trace organic contaminants in soil. DGT
 samplers were deployed in laboratory experiments investigating
 soil-compound interaction during aging. Six soils with different
 physicochemical properties were spiked with 4 PAH compounds (phenanthrene,
 anthracene, fluoranthene and pyrene) with final concentration of 10 mg
 kg-1 and allowed to age for 45 days. DGT sampling was conducted at time
 intervals, to investigate PAH
 
 adsorption/desorption behaviour and to derive kinetic information on their
 release from the soil solid phase. Soil physical and chemical properties
 such as pH, TOC, soil particle size and the properties of PAHs themselves
 all influenced compound behaviour during the aging process. The ability of
 most of the soils to resupply PAHs from the solid phase to the soil
 solution decreased with aging time. The DGT-induced fluxes in soils (DIFS)
 model was used to obtain information on PAH desorption kinetics from the
 soil solid phase to the soil solution phase. Desorption kinetics and the
 labile pool size both affected the ability of soils to re-supply PAHs. The
 labile pool size was affected by pH and TOC.
 
 
 DGT has been used to explore the relationship between soil and crop plant
 uptake of PAHs substances. An experiment was conducted, growing lettuce,
 radish and maize in six different soils, spiked initially with 10 mg kg-1
 of 4 PAHs. DGT sampling was performed before planting and after
 harvesting, together with sampling of soil solution and a sequential
 extraction procedure. DGT measurements showed changes of the resupply of
 PAHs from the soil solid phase before and after crops planting. The
 presence of PAHs in the air affected the PAH content of aboveground plant
 parts. PAHs sampled by DGT, and in soil solution and in the sequential
 extraction procedure were compared to crop concentrations. None of the
 soil tests gave clear correlations to the plant concentrations. Possible
 reasons for this were discussed and recommendations were made for further
 studies. The thesis provides the foundation for future work on using DGT
 to further investigate PAHs (and other compounds) in the environment.
 Recommendations are made for applications of DGT to
 
 provide novel insights on the sources, fates and behaviour of PAHs in the
 environment.