Bioaccessibility of Metals in Soils at Typical Legacy Industrial Sites: In Vitro Evaluation Using Physiologically-Based Extraction.

Risk assessment of soil metal pollution based on total metal contents might give overestimates by neglecting the bioaccessibility of the pollutants to soil biota. Physiologically-based extraction tests (PBET) are in vitro methods for evaluation of bioaccessibility of soil pollutants. A total of 27 soil samples collected from four types of legacy industrial site representing metal smelting, lead-acid battery factories, chemical plants and steel plants were analyzed for the bioaccessibility of six potentially toxic metals using a PBET method. The metal pollutants at the industrial sites depended on the former industrial processes and emissions. The highest proportions of gastric phase and intestinal phase in these soil samples were 43.9% for Cd and 27% for Cu, respectively. Factors affecting metal bioaccessibility included type of industry and soil properties. The soils at a lead-acid battery factory showed relatively high bioaccessibility of Pb, Zn and Cd and those at the steel plant showed relatively low metal bioaccessibility. Soil organic matter and clay contents were positively related to metal bioaccessibility but soil pH and CEC showed negative relationships. Further studies are recommended to determine the speciation of the bioaccessible metals in these soils.

Quantification of Microplastics in Soils Using Accelerated Solvent Extraction: Comparison with a Visual Sorting Method.

Visual sorting is a method that is widely used in microplastic analysis, but it has limitation in the quantification of small-size microplastics. Accelerated solvent extraction (ASE) which frequently used in the analysis of organic contaminants in soils and sediments was used here for the microplastics quantification. A recovery experiment using different spiked polymeric microplastics separately indicates that ASE was useful in the extraction of low-density and low-melting point polymeric microplastics. High recoveries and low matrix effects were observed for the polyethylene, polypropylene and polystyrene microplastics. A further comparison between ASE and visual sorting was conducted for seven soils from agricultural land used for long-term mulching with plastic films. The results confirmed that ASE was capable of microplastics quantification for farmland soils and polyethylene film in the ASE extracts could be identified by Fourier transform infrared spectroscopy. Meanwhile, ASE conducted on small samples (3.0 g) gave results that showed close agreement with the visual sorting method.

Response of soil enzyme activities and bacterial communities to the accumulation of microplastics in an acid cropped soil.

The ecological stress of microplastics (MPs) contamination in agroecosystems raise worldwide concerns. However very few studies concentrated on the effects of MPs exposure on soil microbial community. The alterations of enzymatic activities and bacterial communities were assayed by spiking 1% and 5% (w/w) of polyethylene (PE) and polyvinyl chloride (PVC) MPs in an acid soil. The results showed that both PE and PVC addition inhibited fluorescein diacetate hydrolase activity and stimulated urease and acid phosphatase activities, and declined the richness and diversity of the bacterial communities. More severe effects were observed in the PE treated soils compared to the PVC treated soils generally. The relative abundances of families Burkholderiaceae increased significantly (p < .05) after MPs addition, suggesting the bacteria associated with nitrogen fixation stimulated by the MPs input. Meanwhile, significant (p < .05) decline of Sphingomonadaceae and Xanthobacteraceae after addition of 5% PVC and 1% PE MPs, respectively implied that MPs might inhibit the biodegradation of xenobiotics in the soil. Mover, the PICRUSt analysis demonstrated that membrane transporter was a sensitive prediction functional gene of microplastics exposure in the soil. Future studies could be focused on the role of MPs on the regulation of nitrogen cycling and organic compounds degradation in soils.