Approved Abstracts

Evaluating the toxicity of haloaromatic water disinfection by-products in human placenta and lung cells

Author(s): Instituto de Diagnóstico Ambiental y Estudios del Agua (IDAEA) -CSIC-; IDAEA -CSIC-; IDAEA -CSIC-; IDAEA -CSIC-; IDAEA -CSIC-;
Presenter: Cinta Porte

Disinfection of drinking water generates hundreds of disinfection byproducts (DBPs). Among them, haloaromatic DBPs, are still poorly investigated. They are suspected to be more toxic than haloaliphatic ones and are currently not regulated. Thus, this work aims to investigate their comparative toxicity and ability to generate oxidative stress and alter the expression of genes involved in xenobiotic (cyp1a1) and steroid metabolism (cyp19a1, hsd17b1, hsd17b12 and hsd3b1) in human placental JEG-3 cells. In addition, genotoxicity was evaluated in human alveolar cells A549 as the formation of micronuclei after cell division. Halobenzoquinones (2,6-dichloro- and 2,6-dibromo-1,4-benzoquinone (DCBQ, DBBQ)) showed the highest cytotoxicity (EC50: 18 to 26 µg/mL) and induced very high levels of reactive oxygen species (ROS) -up to 80-fold- in exposed cells. Such high levels of ROS can cause oxidative stress and are probably associated with the rapid metabolism of halobenzoquinones in JEG-3 cells, confirmed by the up-regulation of cyp1a1 expression (up to 100-fold) after 24 h exposure. Furthermore, DBBQ and DCBQ significantly up-regulated the expression of genes involved in estrogen synthesis in placenta (cyp19a1, hsd17b1 and hsd3b1 and hsd17b12). The rest of DBPs tested showed low or not significant cytotoxicity (EC50 ≥ 100 µg/mL), although 2,4,6-trichloro- and 2,4,6-tribromo-phenol (TCP, TBP), 3,5-dichloro- and 3,5-dibromo-4-hydroxybenzaldehyde (DCHBA, DBHBA), and 3,5-dichloro-salicylic acid (DCSA) also induced ROS generation (up to 2.5-fold), the expression of cyp1a1 (up to 30-fold) and the expression of steroid metabolic genes (up to 5-fold). The up-regulation of enzymes involved in the synthesis of estrogens shows that haloaromatic DBPs can act as endocrine disrupters by altering the steroid balance in placenta, which is necessary for normal embryonic and fetal development. Regarding genotoxicity, TCP, TBP and DBHB induced the formation of micronuclei in A549 lung cells at concentrations well above those described in water (100 µg/mL, 350 to 500 µM). These results show low genotoxic potential of haloaromatic DBPs in comparison to haloacetic acids, which induced the generation of micronuclei at concentrations 30 to 50-fold lower. This study highlights the different modes of action haloaromatic DBPs, and the comparatively high toxicity of halobenzoquinones, particularly in terms of alterations of placenta steroid metabolism and generation of oxidative stress.

Keywords: Disinfection byproducts; endocrine disruption; oxidative stress




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