Mercury (Hg) Contaminated Sites in Kazakhstan: Review of Current Cases and Site Remediation Responses

Mercury (Hg) emissions from anthropogenic sources pose a global problem. In Central Asia, Kazakhstan's central and northern regions are among the most severely Hg-contaminated territories. This is due to two former acetaldehyde (in Temirtau) and chlor-alkali (in Pavlodar) plants, discharges from which during the second half of the 20th century were estimated over 2000 tons of elemental Hg. However, the exact quantities of Hg released through atmospheric emissions to the environment, controlled discharges to the nearby aquatic systems, leakages in the cell plant, and contaminated sludge are still unknown. The present review is the initiation of a comprehensive field investigation study on the current state of these contaminated sites. It aims to provide a critical review of published literature on Hg in soils, sediments, water, and biota of the impacted ecosystems (Nura and Irtysh rivers, and Lake Balkyldak and their surrounding areas). It furthermore compares these contamination episodes with selected similar international cases as well as reviews and recommends demercuration efforts. The findings indicate that the contamination around the acetaldehyde plant site was significant and mainly localized with the majority of Hg deposited in topsoils and riverbanks within 25 km from the discharge point. In the chlor-alkali plant site, Lake Balkyldak in North Kazakhstan is the most seriously contaminated receptor. The local population of both regions might still be exposed to Hg due to fish consumption illegally caught from local rivers and reservoirs. Since the present field data is limited mainly to investigations conducted before 2010 and given the persisting contamination and nature of Hg, a recent up-to-date environmental assessment for both sites is highly needed, particularly around formerly detected hotspots. Due to incomplete site remediation efforts, recommendations given by several researchers for the territories of the former chlor-alkali and acetaldehyde plant site include ex-situ soil washing, soil pulping with gravitational separation, ultrasound and transgenic algae for sediments, and electrokinetic recovery for the former and removal and/or confinement of contaminated silt deposits and soils for the latter. However, their efficiency first needs to be validated. Findings and lessons from these sites will be useful not only on the local scale but also are valuable resources for the assessment and management of similar contaminated sites around the globe.

Potentially toxic elements in toys and children's jewelry: A critical review of recent advances in legislation and in scientific research

Contamination by potentially toxic elements (PTEs) in children's toys and jewelry is an ongoing problem where PTEs can become bioavailable especially via oral pathway (ingestion as a whole or of parts, and mouthing) and may cause adverse health effects for children. In the present review, legislation updates from the last decade in the United States (U.S.), Canada, and the European Union (E.U.) on PTEs in toys and jewelry are presented. Then, a literature review mostly covering the last decade on the total concentration, bioavailability, children's exposure, and bioaccessibility of PTEs in toys and jewelry is provided. The U.S. and Canadian legislations mainly focus on lead (Pb) and cadmium (Cd) total/soluble concentration limits to prevent exposure and have received several updates within the last decade, extending particularly the covered span of children's products. It seems that the introduction, subsequent enforcement, and update of regulations in developed countries have shifted the problem towards developing countries. In terms of categories, metallic toys and children's jewelry still have the most severe PTE contamination and the presence of Pb and Cd in these articles is an ongoing issue. Some studies suggest that color can be used as an indicator for the potential presence of PTEs (linked to chemicals such as lead chromate, cadmium sulfide) but the evidence is not always clear. Another concern is vintage/second-hand toys and jewelry as those items might have been produced before the legislation was present. As total and bioaccessible concentrations of PTEs in toys and jewelry do not always correlate, approaches considering bioaccessibility (e.g. of the E.U.) are more scientifically appropriate and help with better estimation of risk from exposure. Studies on toy and jewelry contamination using in vitro bioaccessibility techniques has become more common, however, there is still no in vitro test specifically designed and validated for toys and jewelry.