We have performed a study aimed at investigating the critical concentration of urinary cadmium (UCd) required for the development of renal dysfunction. We studied population groups (totally 790 persons) living in two cadmium exposed areas and one control area in China. UCd, was determined as an indicator of cadmium exposure and accumulation, while the concentrations of N-acetyl-beta-D-glucosaminidase (NAG), its iso-form B (NAG-B), beta2-microglobulin (B2M), retinol binding protein (RBP), and albumin (ALB) in urine were measured as indicators of the renal effects caused by cadmium. There was a significantly increased prevalence of hyperNAGuria, hyperNAG-Buria, hyperB2Muria, hyperRBPuria and hyperALBuria with increasing levels of Cd excretion in urine. We used the benchmark dose (BMD) procedure to estimate the critical concentration of urinary cadmium in this general population. The lower confidence limit of the BMD (LBMD-05) of urinary cadmium for a 5% level of risk above the background level was estimated for each of the renal effect indicators. The BMD-05/LBMD-05 were estimated to be 4.46/3.99, 6.70/5.87, 8.36/7.31, 7.98/6.98 and 15.06/12.18 microg/g creatinine for urinary NAG-B, NAG, B2M, RBP and ALB, respectively. Our findings suggest, based on the present study, that the Lower Confidence Limit of the Population Critical Concentration of UCd (LPCCUCd-05) of tubular dysfunction for 5% excess risk level above the background may be ca. 3-4 microg/g creatinine, and that cadmium concentration in urine should be kept below this level to prevent renal tubular damage. This report is the first to use the BMD method in this field and to define the concept of critical concentration in urine.

Aerobic denitrifiers coupled with a denitrification agent were applied in the sediment of an urban river for the bioremediation of nitrogen pollution. The results revealed that 14.7% of the total nitrogen in the sediment was removed after 115 days of treatment and the nitrate nitrogen concentration removal rate was enhanced in the overlying water. Compared with the control, the total transferable nitrogen in the sediment increased from 0.097 to 0.166 mg/g, indicating that more nitrogen is likely to be involved in the biogeochemical cycling of nitrogen. Increased urease activity indicated the possible further potential of nitrogen biodegradation, while the decreased protease pointed to the low concentration of protein remaining in the sediment. Sequencing revealed that the bacterial community diversity in the sediment increased significantly after 43 days of treatment and that the effect persisted. Compared with other microcosms, the dominant phyla in the sediment after 43 days were Firmicutes, Elusimicrobia, Spirochaetae and Fibrobacteres; whereas, after 115 of treatment, the dominant bacteria were Nitrospirae, Deferribacteres and Chloroflexi. The dominant bacteria in the sediment are mainly associated with nitrogen cycling and thus contributed considerably to nitrogen removal in the sediment. Overall, the direction of species succession was similar to natural succession; namely, there were no undesirable ecological risks involved. This study highlights the possible benefits and feasibility of using bioaugmentation technology coupled with biostimulation to remediate nitrogen-polluted sediments.

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Impacts of deposits discharged from a municipal pipe on urban river sediment were investigated in the Hucang River in Tianjin, China. At the outlet of the pump station, the average concentrations of total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) in the sediment increased sharply from 2390, 799, and 14,600 mg/kg to 6500, 3700, and 153,000 mg/kg, respectively, and remained stable at high level after the rainy season. A portion of pollutants would migrate along the river, and the concentration was usually in a negative relationship with the distance. The average Shannon-Wiener value on the upstream section was higher than those on the downstream sections. This revealed that the deposits discharged decreased the bacterial diversity in the sediment, and high concentrations of pollutants may markedly change the bacterial community structure in the sediment. To reduce the pollution of the urban river after rainy season, four kinds of microbial consortiums A (Zhangda), B (Aiersi), C (Qinghe), and D (Inpipe) were applied to bioremediate the polluted sediment in lab scale. Bioaugmentation with microbial consortium A showed good performance on the bioremediation of the polluted sediment. The average removal efficiency of TN, TP, and organic matter reached 35.5, 43.7, and 39.1%, respectively, after 22 days of treatment. Moreover, the bacterial evenness and diversity in the sediment markedly increased, indicating that the microbial environment was more favourable after bioaugmentation and sustainable development would be guaranteed. This study improves our understanding of the impacts of deposits discharged from a stormwater drain system on urban river sediment, and explores the effectiveness of bioaugmentation for the bioremediation of polluted sediment, which will provide the basis of sewer deposit pollution control.

Yeast, widely used in wastewater treatment, can make use of organic matter and provide nutrition for other living things. The effect of yeast inoculum addition on the remediation of water and sediment in an urban river was evaluated. In the field test, average removal efficiency of CODCr, NH3‐N, and TN was 20 %, 25 %, and 25 %, respectively, in the addition segment after 12 days. After one year, the concentrations of TN and TOC in sediment were not significantly different between the addition and upstream segments. However, species of carbon chains, alkanes with lower boiling points, fatty acids, and esters increased significantly in the sediment after yeast addition, indicating a long‐term effect on remediation by increasing biodegradability. Based on two years of long‐term monitoring, the total numbers of bacteria, actinomycetes, and fungi in the sediment from the yeast addition segment were greater than those of the upstream segment. The sequencing results showed that the diversity of bacteria in the addition segment was better than that in the upstream segment. In summary, yeast addition had a significant effect on remediation in an urban river by increasing microbial number and diversity and providing a more favourable microbial environment.

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