Current status and prospects of research on 1,4-dioxane pollution and treatment technologies in the water environment

1,4-dioxane pollution is characterized by its early identification, widespread sources and extensive distribution. The pollutant is highly mobile and persistent in the water environment and is classified as a B2(probable) human carcinogen. After reviewing recent researches on the pollution status,transport and transformation characteristics of 1,4-dioxane in the water environment, as well as the environmental pollution remediation and treatment technologies, and the status of environmental regulation,this paper addresses that the distribution of 1,4-dioxane in water bodies is significantly correlated with chlorinated hydrocarbon pollutants such as 1,1,1-trichloroethane(1,1,1-TCA) and trichloroethylene(TCE).It is noteworthy that 1,4-dioxane often occurs in symbiosis with 1,1,1-TCA and has a similarity contamination plume distribution to 1,1,1-TCA. The natural attenuation of 1,4-dioxane in groundwater environment is weak, but there is a certain degree of biological oxidation attenuation. Current methods for treating 1,4-dioxane pollution mainly include extraction-treatment technology, advanced oxidation treatment technology, modified biological treatment technology and phytoremediation technology, all of which have their limitations in practical application. Currently, there is no environmental regulation available for the 1,4-dioxane pollution worldwide, and no enforceable standard established for defining the health trigger levels of 1,4-dioxane in drinking water. Research on this contaminant in China is generally limited to the site or laboratory scale, and there are no studies on the environmental risk and quality standards for 1,4-dioxane in the water environment.

Arsenic contamination caused by roxarsone transformation with spatiotemporal variation of microbial community structure in a column experiment

Arsenic contamination from roxarsone in livestock manure is common,and livestock manure continuously accumulates in the open environment.Evaluations of the environmental processes of As mobilization and transformation are critical for predicting the fate of As compounds after roxarsone degradation.In this study,spatiotemporal variations in As species and microbial community structure were characterized using laboratory column experiments with background soil collected from Yanggu County(northern Shandong Plain,China),a region of intense poultry production.Organic and inorganic arsenic were detected by high-performance liquid chromatography(HPLC)and HPLC with hydride generation atomic fluorescence spectrometry(HPLC-HG-AFS),respectively.High-throughput sequencing technology was used to describe microbial diversity.Results showed that roxarsone was transformed completely within 7 days,and A_(s)(Ⅲ)and As(Ⅴ)were the major degradation products.The concentration of A_(s)(Ⅲ)was much lower than that of As(Ⅴ).The A_(s)(Ⅲ)concentration increased significantly after Day 14,whereas the A_(s)(Ⅴ)concentration increased significantly after Day 84,indicating that A_(s)(Ⅲ)was initially produced.The microbial community structure changed significantly as roxarsone transformed into various As compounds.A critical and dominant bacterial strain,norank_f__Family_XVⅢ,was found to be related to the degradation of roxarsone into As(Ⅲ).This study improves our understanding of the fate of As species released from poultry litter to soil and groundwater,which is a threat to human health and environment.

Transformation of ammonium nitrogen and response characteristics of nitrifying functional genes in tannery sludge contaminated soil

High concentrations of ammonium nitrogen released from tannery sludge during storage in open air may cause nitrogen pollution to soil and groundwater.To study the transformation mechanism of NH_(4)^(+)-N by nitrifying functional bacteria in tannery sludge contaminated soils,a series of contaminated soil culture experiments were conducted in this study.The contents of ammonium nitrogen(as NH_(4)^(+)-N),nitrite nitrogen(as NO_(2)^(−)-N)and nitrate nitrogen(as NO_(3)^(−)-N)were analyzed during the culture period under different conditions of pollution load,soil particle and redox environment.Sigmodial equation was used to interpret the change of NO_(3)^(−)-N with time in contaminated soils.The abundance variations of nitrifying functional genes(amoA and nxrA)were also detected using the real-time quantitative fluorescence PCR method.The results show that the nitrification of NH_(4)^(+)-N was aggravated in the contaminated silt soil and fine sand under the condition of lower pollution load,finer particle size and more oxidizing environment.The sigmodial equation well fitted the dynamic accumulation curve of the NO_(3)^(−)-N content in the tannery sludge contaminated soils.The Cr(III)content increased with increasing pollution load,which inhibited the reproduction and activity of nitrifying bacteria in the soils,especially in coarse-grained soil.The accumulation of NO_(2)^(−)-N contents became more obvious with the increase of pollution load in the fine sand,and only 41.5%of the NH_(4)^(+)-N was transformed to NO_(3)^(−)-N.The redox environment was the main factor affecting nitrification process in the soil.Compared to the aerobic soil environment,the transformation of NH_(4)^(+)-N was significantly inhibited under anaerobic incubation condition,and the NO_(3)^(−)-N contents decreased by 37.2%,61.9%and 91.9%under low,medium and high pollution loads,respectively.Nitrification was stronger in the silt soil since its copy number of amoA and nxrA genes was two times larger than that of fine sand.Moreover,the copy numbers of amoA and nxrA genes in the silt soil under the aerobic environment were 2.7 times and 2.2 times larger than those in the anaerobic environment.The abundance changes of the amoA and nxrA functional genes have a positive correlation with the nitrification intensity in the tannery sludge-contaminated soil.