Thousands of organic micropollutants
and their transformation products
occur in water. Although often present at low concentrations, individual
compounds contribute to mixture effects. Cell-based bioassays that
target health-relevant biological endpoints may therefore complement
chemical analysis for water quality assessment. The objective of this
study was to evaluate cell-based bioassays for their suitability to
benchmark water quality and to assess efficacy of water treatment
processes. The selected bioassays cover relevant steps in the toxicity
pathways including induction of xenobiotic metabolism, specific and
reactive modes of toxic action, activation of adaptive stress response
pathways and system responses. Twenty laboratories applied 103 unique
in vitro bioassays to a common set of 10 water samples collected in
Australia, including wastewater treatment plant effluent, two types
of recycled water (reverse osmosis and ozonation/activated carbon
filtration), stormwater, surface water, and drinking water. Sixty-five
bioassays (63%) showed positive results in at least one sample, typically
in wastewater treatment plant effluent, and only five (5%) were positive
in the control (ultrapure water). Each water type had a characteristic
bioanalytical profile with particular groups of toxicity pathways
either consistently responsive or not responsive across test systems.
The most responsive health-relevant endpoints were related to xenobiotic
metabolism (pregnane X and aryl hydrocarbon receptors), hormone-mediated
modes of action (mainly related to the estrogen, glucocorticoid, and
antiandrogen activities), reactive modes of action (genotoxicity)
and adaptive stress response pathway (oxidative stress response).
This study has demonstrated that selected cell-based bioassays are
suitable to benchmark water quality and it is recommended to use a
purpose-tailored panel of bioassays for routine monitoring.
Numerous studies have identified the presence and bioactivity of glucocorticoid receptor (GR) active substances in water; however, the identification and activity-balance of GR compounds remained elusive. This study determined the occurrence and attenuation of GR bioactivity and closed the balance by determining those substances responsible. The observed in vitro GR activity ranged from 39 to 155 ng dexamethasone-equivalent/L (ng Dex-EQ/L) in the secondary effluents of four wastewater treatment plants. Monochromatic ultraviolet light of 80 mJ/cm(2) disinfection dose was efficient for GR activity photolysis, whereas chlorination could not appreciably attenuate the observed GR activity. Ozonation was effective only at relatively high dose (ozone/TOC 1:1). Microfiltration membranes were not efficient for GR activity attenuation; however, reverse osmosis removed GR activity to levels below the limits of detection. A high-sensitivity liquid chromatography with tandem mass spectrometry (LC-MS/MS) method was then developed to screen 27 GR agonists. Twelve were identified and quantified in effluents at summed concentrations of 9.6-21.2 ng/L. The summed Dex-EQ of individual compounds based on their measured concentrations was in excellent agreement with the Dex-EQ obtained from bioassay, which demonstrated that the detected glucocorticoids can entirely explain the observed GR bioactivity. Four synthetic glucocorticoids (triamcinolone acetonide, fluocinolone acetonide, clobetasol propionate, and fluticasone propionate) predominantly accounted for GR activity. These data represent the first known publication where a complete activity balance has been determined for GR agonists in an aquatic environment.
With burgeoning population and diminishing availability of freshwater resources, the world continues to expand the use of alternative water resources for drinking, and the quality of these sources has been a great concern for the public as well as public health professionals. In vitro bioassays are increasingly being used to enable rapid, relatively inexpensive toxicity screening that can be used in conjunction with analytical chemistry data to evaluate water quality and the effectiveness of water treatment. In this study, a comprehensive bioassay battery consisting of 36 bioassays covering 18 biological endpoints was applied to screen the bioactivity of waters of varying qualities with parallel treatments. Samples include wastewater effluent, ultraviolet light (UV) and/or ozone advanced oxidation processed (AOP) recycled water, and infiltrated recycled groundwater. Based on assay sensitivity and detection frequency in the samples, several endpoints were highlighted in the battery, including assays for genotoxicity, mutagenicity, estrogenic activity, glucocorticoid activity, aryl hydrocarbon receptor activity, oxidative stress response, and cytotoxicity. Attenuation of bioactivity was found to be dependent on the treatment process and bioassay endpoint. For instance, ozone technology significantly removed oxidative stress activity, while UV based technologies were most efficient for the attenuation of glucocorticoid activity. Chlorination partially attenuated genotoxicity and greatly decreased herbicidal activity, while groundwater infiltration efficiently attenuated most of the evaluated bioactivity with the exception of genotoxicity. In some cases, bioactivity (e.g., mutagenicity, genotoxicity, and arylhydrocarbon receptor) increased following water treatment, indicating that transformation products of water treatment may be a concern. Furthermore, several types of bioassays with the same endpoint were compared in this study, which could help guide the selection of optimized methods in future studies. Overall, this research indicates that a battery of bioassays can be used to support decision-making on the application of advanced water treatment processes for removal of bioactivity.
This
study reveals key disinfection byproduct (DBP) toxicity drivers
in drinking water across the United States. DBPs, which are ubiquitous
in drinking water, form by the reaction of disinfectants, organic
matter, bromide, and iodide and are generally present at 100–1000×
higher concentrations than other contaminants. DBPs are linked to
bladder cancer, miscarriage, and birth defects in human epidemiologic
studies, but it is not known as to which DBPs are responsible. We
report the most comprehensive investigation of drinking water toxicity
to date, with measurements of extracted whole-water mammalian cell
chronic cytotoxicity, over 70 regulated and priority unregulated DBPs,
and total organic chlorine, bromine, and iodine, revealing a more
complete picture of toxicity drivers. A variety of impacted waters
were investigated, including those impacted by wastewater, agriculture,
and seawater. The results revealed that unregulated haloacetonitriles,
particularly dihaloacetonitriles, are important toxicity drivers.
In seawater-impacted water treated with chloramine, toxicity was driven
by iodinated DBPs, particularly iodoacetic acids. In chlorinated waters,
the combined total organic chlorine and bromine was highly and significantly
correlated with toxicity (r = 0.94, P < 0.01); in chloraminated waters, total organic iodine was highly
and significantly correlated with toxicity (r = 0.80, P < 0.001). These results indicate that haloacetonitriles
and iodoacetic acids should be prioritized in future research for
potential regulation consideration.
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