Occurrence, distribution characteristics and exposure assessment of perchlorate in the environment in China

Recognizing the extent of perchlorate pollution in the environment is critical to preventing and mitigating potential perchlorate harm to human health. The presence and distribution of perchlorate in Chinese environmental matrixes (water, atmosphere, and soil) were systematically investigated and comprehensively analyzed, and cumulative perchlorate exposure at the regional level was assessed using a combined aggregate exposure pathway method. The results showed that perchlorate is ubiquitous in the environment of China with significant regional differences. The total perchlorate exposure levels in each region of China ranked as South China > Southwest China > East China > North China > Northeast China > Northwest China. Although the average exposure dose of 0.588 (95 %CI: 0.142 -1.914) μg/kg bw/day being lower than the reference dose of 0.70 μg/kg bw/day, it was observed that the intake of perchlorate in some regions exceed this reference dose. Oral ingestion was the primary route of perchlorate exposure (89.97-96.57 % of the total intake), followed by dermal contact (3.21-9.16 %) and respiratory inhalation. Food and drinking water were the main sources of total perchlorate intake, contributing 52.54 % and 31.12 % respectively, with the latter contributing significantly more in southern China than in northern China. In addition, perchlorate exposure from dust sources was also noteworthy, as its contribution was as high as 23.18 % in some regions. These findings will improve understanding of the perchlorate risk and serve as a critical reference for policymakers in crafting improved environmental management and risk mitigation strategies in China and other nations.

Chlorate addition enhances perchlorate reduction in denitrifying membrane-biofilm reactors

Perchlorate is a widespread drinking water contaminant with regulatory standards ranging from 2 to 18 μg/L. The hydrogen-based membrane-biofilm reactor (MBfR) can effectively reduce perchlorate, but it is challenging to achieve low-µg/L levels. We explored chlorate addition to increase the abundance of perchlorate-reducing bacteria (PRB) and improve removals. MBfR reactors were operated with and without chlorate addition. Results show that chlorate doubled the abundance of putative PRB (e.g., Rhodocyclales) and improved perchlorate reduction to 23 ± 17 µg/L, compared to 53 ± 37 µg/L in the control. Sulfate reduction was substantially inhibited during chlorate addition, but quickly recovered once suspended. Our results suggest that chlorate addition can enhance perchlorate reduction by providing a selective pressure for PRB. It also decreases net sulfate reduction. KEY POINTS: • Chlorate increased the abundance of perchlorate-reducing bacteria • Chlorate addition improved perchlorate removal • Chlorate appeared to suppress sulfate reduction.

Topological Sustainability of Crop Water Requirements and Irrigation Scheduling of Some Main Crops Based on the Penman-Monteith Method

The following method was used to apply the topology of the current study of evapotranspiration ETo, net irrigation demand, irrigation schedules, and total effective rain fall of different crop models: using the Food and Agriculture Organization's (FAO) CROPWAT 8.0 standard software and the CLIMWAT 2.0 tool and the FAO-56 Penman-Monteith approach to examine the variable topology of evapotranspiration ETo. Due to high temperatures in summer with an annual mean of 6.33 mm/day, the topological demonstration of reference evapotranspiration (ETo) increases from 2.84 mm/day in January to a maximum of 9.61 mm/day in July. Effective rainfall fluctuates from 0 mm to 53.4 mm. Total irrigation topological indices requirements were 308.3 mm/dec, 335.9 mm/dec, 343.6 mm/dec, 853 mm/dec, and 1479.6 mm/dec for barley, wheat, maize, rice, and citrus, respectively. The physical topological indices due to low demand in winter and high demand in summer, the total net irrigation, and gross irrigation for clay loamy soils for wheat (210.6 mm and 147.4 mm), barley (176.6 mm and 123.6 mm), citrus (204.5 mm and 143.2 mm), and maize (163.9 mm and 114.7 mm), but not for rice. This topology demonstrates that wheat has 4, barley has 4, citrus has 12, maize has 4, and rice crop has 12 irrigation schedules in a year.