A study on the physico-chemical speciation of heavy metals in waters of rivers, and lakes in the Changjiang River Valley, China
In the aquatic system, heavy metals always exist in a number of physico-chemical forms: particulate (Cp), soluble which consists of labile (MALI) and bound (inorganic MAb and organic MLb). The environmental behaviors of a metal are critically dependent on these forms. In this paper, the forms of heavy metals in waters from the Changjiang River source to mainstream and lakes were determined by ASV method. The main results are as follows: 1. The total contents (Ct) of Zn, Pb, Cu and Cd in the source were 4.0, 1.88, 1.28 and 0.07 (μg/L) respectively, while Ct (μg/L) in the mainstem were in the order of Zn (20.1) > Cu (14.9) > Pb (6.73) > Cd (0.15). Ct (μg/L) in Dianchi Lake were Zn (7.2) > Pb (0.72) > Cu (0.53) > Cd (0.05), and in Poyang Lake were Zn (12.5) > Pb (4.2) > Cu (3.4) > Cd (0.05), and in Poyang Lake were Zn (12.5) > Pb (4.2) > Cu (3.4) > Cd (0.05). However, most of them were presented as Cp. Their dissolved contents (Cs, μ/L) were lower. 2. The distribution of soluble forms was related to the type of metal and to environmental variables. In general, Zn and Cd have a tendency to be present in MALi, Pb in MAb and Cu in MLb.
Evaluation of water quality pollution indices for heavy metal contamination monitoring. A study case from Akpabuyo-Odukpani area, Lower Cross River Basin (southeastern Nigeria)
Two documented methods, Contamination index (Cd) and the Heavy metal potential index (HPI) were evaluated for their suitability for contamination monitoring of surface water in parts of southeastern Nigeria. Results show that despite the significant correlation between the data generated from these indices, the final classification gave two extreme results. Thus a third model (Heavy metal evaluation index, HEI) was developed to accommodate this deficiency. The HEI values show significant correlation with Cd and HPI but categorised into semi quantitative classes for proper assessment of pollution level. The HEI values show that 65.5% of the sites are classed as low with values lower than the mean and the remaining 34.5% with values greater than the mean are classed as medium. In contrast, water samples from all the 32 locations were classified as high and low using the Cd and the HPI respectively. However, a reclassification of the Cd and HPI categories using the mean values as a criteria show good comparison with the HEI. The differences in the former can be attributed to the variations in the concentrations of the heavy metals used for the different evaluation schemes.
Dissolved zinc in rivers
Reliable measurements of the concentrations of dissolved trace metals in rivers are needed for calculating oceanic chemical mass balances, understanding continental weathering and freshwater chemistry, and evaluating anthropogenic chemical perturbations. For dissolved zinc, it has been suggested1 that typical river concentrations are as high as 450 nmol kg−1. However, it has also been proposed2 that most published values are incorrect and the true value of dissolved zinc may be 2 orders of magnitude lower. Because zinc is one of the most commonly used metals in the industrial world, the sampling and analysis of this element in natural waters is particularly prone to contamination2. We present here the dissolved zinc concentrations from various rivers draining both pristine and industrially influenced environments. These samples were collected and analysed by methods that have yielded reliable oceanic data for other metals3. The data indicate that in relatively undisturbed systems dissolved zinc concentrations are typically only 10−9–10−8 mol kg−1, with some dependence of concentration on pH. In industrially influenced river systems, however, zinc concentrations can be 1–2 orders of magnitude higher.