Water quality degradation drives the release and fractionation transformation of trace metals in sediment.

The behavior and stability of trace metals in sediment are important to the ecology of rivers. Deteriorated water quality from domestic wastewater discharge has been studied extensively, but the effect of domestic wastewater on trace metals in sediment is poorly understood. To investigate this, we simulated the water quality degradation process through leaching experiments using domestic wastewater as the leaching solution. The results indicated that domestic wastewater does not negatively influence the stability and fractionation of trace metals in this experimental model, the existence of phosphate was the pacing factor for this phenomenon. Single-factor control treatment groups showed that a leaching solution with pH < 6, NaCl, NH4Cl, NaNO3, and humic acid promoted the dissolution of trace metals from sediment, whereas NaH2PO4 inhibited this process and increased their stability in sediment. The response of trace metals behavior to NaCl, NH4Cl, and extreme pH levels was more sensitive than NaNO3 and HA. Chloride ions can form relatively stable compounds with trace metals, reducing the activity of trace metals in the solution and promoting the release of trace metals from sediment, but it has positive effect on Pb and Zn stability and negative effect on Cu. Extreme pH conditions (pH > 10) and higher concentrations of leaching solutions (NaCl, NH4Cl, NaNO3, and HA) led to an increase in the Cu leaching concentration from sediment and the transformation to unstable fractions, while the impact on the stability of Zn and Pb was beneficial or had little effect. These experiment groups indicated that phosphate is beneficial to the stability of trace metals even at the condition of water degradation and can decrease the ecological risk caused by trace metals.

[Effects of supplementation of different kinds of iodine on the antioxidative ability of retina in iodine deficient rats].

OBJECTIVE: To study the effects of iodine supplementation (in different kinds and doses) on the antioxidative ability of retina in iodine deficient rats. METHODS: One hundred and twenty eight iodine deficient Wistar rats were randomly divided into four groups, normal dose of iodate, normal dose of iodide, high dose of iodate and high dose of iodide. Concentration of serum thyroid hormones, including total TT(3) and total TT(4), were estimated by radioimmunoassay. GSH-Px, SOD, TAOC activities and MDA content in the retina were determined using biochemical methods in the 22nd week of iodine supplementation. RESULTS: Statistical analysis showed that a significant difference in TT(3) level of serum was observed between animals treated with different doses. Serum TT(3) level in the groups treated with high doses was significantly higher than those with normal doses. However, no statistical difference could be detected at TT(4) level between animals treated with different doses. Different kind of iodine did not affect the level of thyroid hormones. Statistical analysis showed that a difference in SOD activity of retina was observed between animals treated with different doses. SOD activity in the groups with normal doses was significantly higher than that in groups with larger doses. Retina TAOC activity was significantly higher in groups treated with iodide than that in groups of iodate. Although there was no statistical difference in GSH-Px activity between different groups, it showed the same tendency as the SOD and TAOC activities, i.e. GSH-Px activity in the groups of normal doses was higher than that in the groups of high doses. GSH-Px activity in groups of iodide was higher than that in the groups of iodate. There was no significant difference in MDA content among these four groups. CONCLUSIONS: Different iodine and doses have certain effects on the antioxidative ability of retina in iodine deficient rat. The rats supplemented potassium iodide at normal dose showed higher antioxidative ability of the retina than those of the others.