Insights into site-specific influences of emission sources on accumulation of heavy metal(loid)s in soils by wheat grains.

Excessive accumulation of heavy metal(loid)s in agricultural environment usually originates from anthropogenic activities. Both large diversities of emission sources and complexity of plant accumulation challenge the understanding of the site-specific effects of emission sources on heavy metal(loid)s in wheat grains. Herein, both soil samples and wheat grain samples (n = 80) were collected from the farmland of Jiyuan City, China. Soil and grain burdens of heavy metal(loid)s were determined by inductively coupled plasma mass spectrometry (ICP-MS) and/or X-ray fluorescence spectrometry (XRF). The quotients (Q) were developed to indicate relative impacts of industrial plants and traffic to soil sites. Principal component analysis-absolute principal component scores-multivariate linear regression (PCA-APCS-MLR) analysis was conducted to reveal the source contributions to heavy metal(loid)s in grains, considering Q values, soil, and wheat grain data. Results showed that contributions of main sources and factors drastically varied with soil sites, and usually overlapped to different extents. For grain Cd and grain Pb, natural soil silicate (0.066/0.104 mg/kg) and iron-bearing minerals (- 0.044/ - 0.174 mg/kg) contributed to high extents, while metal smelting activities (0.018/0.019 mg/kg) and agronomic activities (- 0.017/ - 0.019 mg/kg) unexpectedly posed low or moderate contributions. The pH-mediated availability of soil Cd (0.035 mg/kg) and the sand-dust weather (0.028 mg/kg) also made considerable contributions to grain Cd. For grain As, both natural soil iron-bearing (- 0.048 mg/kg) and silicate minerals (- 0.013 mg/kg) made negative contributions. The results benefit to the decision-making of pollution remediation of farmland soils in the regional scales.

Effects of methyl-CD and humic acid on hydrolytic degradation of the herbicide diclofop-methyl.

Hydrolytic degradation of the herbicide diclofop-methyl was investigated in the multi-pH deionized water, natural aquatic systems and soil suspensions. Resulting data indicated that the herbicide was stable in the acidic and nearly neutral solutions for at least 15 d. The herbicide diclofop-methyl rapidly dissipated in the natural aquatic systems and soil suspensions with half-lives less than 4 d. Methyl-CD (partially methylated beta-cyclodextrin) improved its hydrolytic degradation in the pH 8 deionized water and natural aquatic systems while humic acid inhibited its hydrolytic degradation at the same conditions. But dissolved organic matter in the natural aquatic systems and soil suspensions increased its hydrolysis. Two catalysis mechanisms were introduced to describe the effects of cyclodextrin and organic matter on its hydrolytic metabolism. Though inorganic ions maybe improved its hydrolysis reaction in the natural aquatic systems, Fe2+ and Cu2+ did not form complexes with the herbicide and had poor influences on its hydrolytic degradation whether cyclodextrin was added or not.