Chlorination of microcystin-LR in natural water: Kinetics, transformation products, and genotoxicity.

Microcystin-LR (MC-LR), a type of cyanotoxin commonly found in natural water bodies (sources of drinking water), poses a threat to human health due to its high toxicity. It is essential to successfully remove this cyanotoxin from drinking water sources. In this study, chlorine was used to oxidize MC-LR in Milli-Q water (MQ) (control test) and natural water collected from Lake Longhu (LLW) as a drinking water source. The removal efficiency, proposed transformation pathways, and genotoxicity were investigated. In the chlorine dose range investigated (4.0 mg L-1 - 8.0 mg L-1), the apparent second-order rate constants for MC-LR chlorination varied from 21.3 M-1s-1 to 31.9 M-1s-1 in MQ, higher than that in LLW (9.06 M-1s-1 to 17.7 M-1s-1) due to a faster chlorine decay attributed to the water matrix (e.g., natural organic matter) of LLW. Eleven transformation products (TPs) of MC-LR were identified in the two waters. The conjugated diene moieties and benzene ring of Adda moiety (3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid), and the double bond of Mdha moiety (N-methyldehydroalanine) were the major susceptible reaction sites. Attacking unsaturated bonds by hydroxyl and chlorine radicals to generate monochloro-hydroxy-MC-LR was the primary initial transformation pathway, followed by nucleophilic substitution, dehydration, and cleavage in MC-LR. Chlorine substitution on the benzene ring was also observed. Based on the bacterial reverse-mutation assay (Ames assay), TPs in treated natural water did not induce genotoxicity/mutagenicity. These findings shed light on the role of chlorination in controlling the risk of cyanotoxins in drinking water treatment plants.

The Potential for Genotoxicity, Mutagenicity and Endocrine Disruption in Triclosan and Triclocarban Assessed through a Combination of In Vitro Methods.

Triclosan and Triclocarban, preservatives widely used in cosmetics and other consumer products, underwent evaluation using a battery of new-approach methodologies in vitro (NAMs). Specifically, the Microplate Ames Test (MPF™ Test, Xenometrix, Allschwil, Switzerland) was employed to assess mutagenicity, the Comet assay in vitro on the HaCat cell line and the Mammalian Chromosome Aberration Test were utilized to evaluate genotoxicity, and the XenoScreen® YES/YAS assay was applied to investigate endocrine disruption. The chemicals did not exhibit any positive responses for mutagenicity. However, the mammalian chromosome aberration test identified both chemicals as being positive for genotoxicity at 10 µg/mL. In the Comet assay, the percentage of DNA in the tail significantly increased in a concentration-dependent manner (at 5 and 10 µg/mL for Triclosan, at 2.5, 5, and 10 µg/mL for Triclocarban). The positive response depended on the increasing concentration and the duration of exposure. Triclosan, but not Triclocarban in any of the endocrine assays performed, indicated a potential for endocrine activity in the anti-estrogenic and anti-androgenic assays. The positive in vitro results detected were obtained for concentrations relevant to final products. The alarming findings obtained with the use of new-approach methodologies (NAMs) justify the current precautionary regulatory approach, limiting the use of these preservatives.

Avaliação da eficiência do tratamento de esgoto doméstico pelo teste do micronúcleo em Oreochromis niloticus (Cichlidae) / Evaluation of the domestic wastewater treatment efficiency by micronucleus test on Oreochromis niloticus (Cichlidae)

RESUMO Este estudo teve por objetivo avaliar a eficiência no tratamento do esgoto doméstico de uma cidade do interior paulista, pela análise de micronúcleos e anormalidades nucleares nos eritrócitos de tilápias expostas ao efluente bruto e ao tratado. Duas coletas foram realizadas: uma na estação chuvosa e outra na estação seca. Foram utilizados três aquários de 20 L nos experimentos, com cinco peixes cada. No primeiro, os animais foram expostos à água de poço artesiano (controle negativo); no segundo, ao esgoto bruto diluído; no terceiro, ao esgoto após tratamento. Decorrido o tempo de exposição (72 h), coletou-se o sangue desses animais para obtenção de lâminas de esfregaço. Os resultados obtidos mostraram efeitos genotóxicos e mutagênicos do efluente bruto, em ambas as coletas; porém, esses efeitos não foram significativos após o tratamento do esgoto, o que mostra que o processo utilizado no tratamento foi eficiente para minimizar tais efeitos.

ABSTRACT This study aimed at evaluating the efficiency in the domestic wastewater treatment from a city of Sao Paulo State (Brazil), by micronuclei and nuclear abnormalities analysis in erythrocytes of tilapias exposed to raw and treated wastewater. Two samples were collected. Three aquariums of 20 L, with five fish each, were used in the bioassays. In the first, the animals were exposed to the artesian water (negative control); in the second, to the diluted raw wastewater; and in the third, to after wastewater treatment. After the exposure time (72 h), the blood was collected for preparing the smear slides. The results showed genotoxic and mutagenic effects of the raw wastewater in both samples, showing that the process used was efficient to minimize these effects.