Shigeki Masunaga

In ecological risk assessment, sum-of-toxic-unit approaches based on measured water quality factors such as trace metals are used to infer ecological impacts in the environment. However, it is uncertain whether the use of such approaches yields accurate risk predictions. To address this issue, we investigated and compared (1) water quality, including trace metals, and (2) benthic macroinvertebrate communities in a northern Japanese river receiving treated discharge from an abandoned mine and in a nearby reference river. As a sum-of-toxic-unit approach, we employed a cumulative criterion unit (CCU), namely, the sum of the ratios of the dissolved concentrations of a metal (Cu, Zn, Cd, or Pb) divided by the US Environmental Protection Agency hardness-adjusted environmental water quality criterion for that metal. Compared with the reference sites, at the metal-contaminated sites, the richness, abundance, and structure of macroinvertebrate communities were little affected, with CCUs of 1.7 to 7.4, suggesting that CCU values exceeding 1 do not always indicate marked adverse impacts on these metrics. Further study is still required to derive a more compelling conclusion on the generally applicable relationships between CCUs and ecological impacts on river invertebrates. This would lead to better ecological risk assessments based on sum-of-toxic-unit approaches.

A comprehensive congener specific assessment of polychlorinated biphenyls (PCBs) was conducted for the first time in Bangladesh. All 209 PCB congeners in the surficial coastal sediments from the coastal areas of Bangladesh were analyzed by GC-MS/MS. The total concentrations of PCBs (∑PCBs) varied from 5.27 to 92.21 and 4.61 to 105.3 ng/g dw in winter and summer, respectively, and the ranges were comparable to or higher than those recorded in the sediments from the coastal areas of India, Korea, China, and Taiwan. The seasonal difference in the levels of PCBs was not statistically significant (p > 0.05). The spatial distribution revealed that the areas with recent urbanization and industrialization (Chittagong, Cox’s Bazar and Sundarbans) were more contaminated with PCBs than the unindustrialized area (Meghna Estuary). Moderately chlorinated (4–6 Cl) homologs dominated PCB profiles. A set of congeners based on their detection frequencies and abundance were identified and categorized as potential environmental marker PCBs, which can be used for the future selective monitoring studies where there would be limitations on whole congener assessment. Ecotoxicologically, the sedimentary PCB concentrations exceeded some of the existing environmental quality standards, suggesting a potential threat to the aquatic organisms in the Bangladeshi coastal areas.

To investigate the effects of cooking on reducing the health risk, the concentrations of total arsenic in raw and cooked rice were measured. Raw rice of two rainfed rice varieties was purchased from market of Dhaka, Bangladesh in 2015. Minikit is a long slender grained popular rice variety in Bangladesh while Kataribhogh is a fine grained aromatic rice which is famous for its aroma and texture. One hundred grams of raw rice was washed with Milli-Q water three times. Then, raw rice was cooked with Milli-Q water: grain ratio of 5:1 in an iron pan covered with lid and the excess water after cooking was decanted. Cooked rice was freeze-dried and ground for arsenic analysis. A microwave digestion was used to digest the rice samples for analysis. Samples were analyzed using inductively coupled plasma mass spectrometer (ICP-MS). The arsenic concentrations in raw rice of Minikit and Kataribhogh in this study were 0.123−0.153 µg g⁻¹ and 0.611−0.783 µg g⁻¹, respectively. On the other hand, the total arsenic contents in cooked rice of Minikit and Kataribhogh were 0.115 ± 0.004 µg g⁻¹ and 0.386 ± 0.004 µg g⁻¹, respectively. There was 17% and 46% reduction of arsenic due to washing and cooking of Minikit and Kataribhogh rice, respectively. Based on the concentration of arsenic in raw and cooked rice, the carcinogenic risk of arsenic via rice ingestion was estimated. The estimated risk of arsenic with cooked rice was 1.2 × 10⁻⁵ and 4.1 × 10⁻⁵ while that of raw rice was 1.5 × 10⁻⁵ and 7.7 × 10⁻⁵ for Minikit and Kataribhogh rice, respectively. The results of this study revealed that health risk assessment on the basis of arsenic content of raw rice would be overestimated than the actual health risk.