Dibutyl Phthalate Contributes to the Thyroid Receptor Antagonistic Activity in Drinking Water Processes

Abstract

It has long been recognized that thyroid hormone (TH) is essential for normal brain development in both humans and animals, and there is growing evidence that environmental chemicals can disrupt the thyroid system. In the present work, we used a two-hybrid yeast assay to screen for agonistic or antagonistic thyroid receptor (TR) mediated effects in drinking waters. We found no TR agonistic, but TR antagonistic activities in all samples from the drinking water processes. The TR antagonistic activities in organic extracts of water samples were then calibrated regarding to a known TR-inhibitor, NH3, and were expressed as the NH3 equivalents (TEQbio). The observed TEQbio in waters ranged from 180.8 ( 24.8 to 280.2 ( 48.2 µg/L NH3. To identify the specific compounds responsible for TR disrupting activities, the concentrations of potentially thyroid-disrupting chemicals including organochlorine pesticides (OCPs), phenols, and phthalates in organic extracts were quantitatively determined and their toxic equivalents with respect to NH3 (TEQcal) were estimated from their concentrationdependent relationships, respectively, using the same set of bioassays. Based on the TEQ approach, it was revealed that dibutyl phthalate (DBP) accounted for 53.7 ( 8.2% to 105.5 ( 16.7% of TEQbio. There was no effective removal of these potential thyroid disrupting substances throughout drinking water treatment processes.

Identification of Thyroid-Receptor Antagonists in Water from the Guanting Reservoir, Beijing, China

“…The TEQ developed during the last two decades has been formally adopted by numerous countries for risk assessment and management purposes, which have evolved for dioxins/dioxin-like compounds, estrogenic compounds, and thyroid-disrupting chemicals (Li et al 2010b;Qiao et al 2006). In the present study, for ease of comparison, the results in the bioassays were expressed as the toxic equivalent concentrations that account for the concentration of a reference chemical, AH.…”

“…1. Each sample (10.5 L for the bioassay and 10 L for chemical analysis) was collected in precleaned amber glass bottles as described by Li et al (2010b).…”

“…The concentration-dependent responses curve of organic extracts were expressed and then converted to AH equivalent concentrations (TEQ bio-organic extracts ) (Li et al 2011). Third, the toxic equivalents with respect to the AH of the detected OCPs, phenols, and PAEs (TEQ cal ) were calculated from their concentrations in the water samples (Li et al 2010b). Last, the contribution of each putative TR antagonist to the TEQ bio was estimated.…”

“…Their TEQ cals-OCPs and Phenols were estimated to account for \5.0 % of the total TEQ bio-water sample , suggesting that these two types of chemicals may not contribute to the observed antagonistic TR activities. Some PAEs, such as dibutyl phthalate (DBP) and diethyl hexyl phthalate (DEHP), have been reported to exhibit antithyroid hormone effects and contribute to the observed antagonistic TR activities of drinking water and water sources (Shi et al 2011;Li et al 2010b). Another PAE, benzyl butyl phthalate (BBP), was also reported to be a TR antagonist (Li et al 2014).…”

“…However, identifying the specific compounds responsible for TR-disrupting activities remains challenging. Currently, the most prevailing methodological approach assesses the disrupting effects of organic extracts from environmental samples using bioassays, analyzes incorporated TDCs in organic extracts using instrumental analysis, and uses the TEQ approach to identify the responsible compounds (Shi et al 2011(Shi et al , 2012Li et al 2010b). However, the identified responsible compounds in organic extracts probably do not sufficiently represent whole water samples, which contain not only organic but also inorganic pollutants.…”