BackgroundHydroxylated polybrominated diphenyl ethers (HO-PBDEs) may disrupt thyroid hormone status because of their structural similarity to thyroid hormone. However, the molecular mechanisms of interactions with thyroid hormone receptors (TRs) are not fully understood.ObjectivesWe investigated the interactions between HO-PBDEs and TRβ to identify critical structural features and physicochemical properties of HO-PBDEs related to their hormone activity, and to develop quantitative structure–activity relationship (QSAR) models for the thyroid hormone activity of HO-PBDEs.MethodsWe used the recombinant two-hybrid yeast assay to determine the hormone activities to TRβ and molecular docking to model the ligand–receptor interaction in the binding site. Based on the mechanism of action, molecular structural descriptors were computed, selected, and employed to characterize the interactions, and finally a QSAR model was constructed. The applicability domain (AD) of the model was assessed by Williams plot.ResultsThe 18 HO-PBDEs tested exhibited significantly higher thyroid hormone activities than did PBDEs (p < 0.05). Hydrogen bonding was the characteristic interaction between HO-PBDE molecules and TRβ, and aromaticity had a negative effect on the thyroid hormone activity of HO-PBDEs. The developed QSAR model had good robustness, predictive ability, and mechanism interpretability.ConclusionsHydrogen bonding and electrostatic interactions between HO-PBDEs and TRβ are important factors governing thyroid hormone activities. The HO-PBDEs with higher ability to accept electrons tend to have weak hydrogen bonding with TRβ and lower thyroid hormone activities.

Amorphous forms of natural and synthetic Fe oxyhydroxides and synthetic Mn oxyhydroxides were used to study the Ž . oxidation of antimonite, Sb III , at different pH values. Sb species were measured by differential pulse adsorptive stripping Ž . Ž . Ž . voltametry DPACSV . The oxidation of Sb III to Sb V was always rapid and completed after a few days following pseudo-first order rate laws. A slightly slower oxidation rate was observed at lower pH and was attributed to the lower Ž . stability of the oxyhydroxide compounds under mildly acidic conditions. The oxidation pseudo-first order rate of Sb III by natural Fe oxyhydroxides was also slower when compared to synthetic Fe compounds. This could be explained by a slight Ž . crystallinity of the natural oxides when compared to amorphous synthetic compounds and by their more complex chemical composition which can include adsorbed ions and organic matter. The study confirms that amorphous Fe and Mn oxyhydroxides present in natural waters and sediments can play a detoxifying role by adsorbing and oxidizing the more toxic Ž . Ž . Sb III into Sb V . q

The chlorophenol pollutants (CPs) have been reported to occur at relatively high concentrations in some Chinese waters. To map the distribution of CPs in the surface water throughout China, samples were collected from over 600 sites in the seven major watersheds and three drainage areas. The samples were analyzed for the representative CPs including 2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol. In general, it was observed that 2,4-dichlorophenol and 2,4,6-trichlorophenol were more frequently detected at higher concentrations in the rivers of North China compared with those of South China. High concentration sites of 2,4-dichlorophenol and 2,4,6-trichlorophenol mainly occurred in the Yellow River, Huaihe River, and Haihe River watersheds, while pentachlorophenol contamination mainly occurred in the Yangtze River watershed. The pentachlorophenol was the most ubiquitous CPs being detected in 85.4% of samples (median = 50.0 ng l ). The results of this investigation indicated that 2,4-dichlorophenol and 2,4,6-trichlorophenol contaminations of Yellow River, Huaihe River, and Haihe River watersheds were of particular concern, while the pentachlorophenol contamination mainly occurred in the Yangtze River watershed. These results showed that CPs contamination in the surface water of China was similar to other places of the world.

The biogeochemical cycling and chemical transformation of Se in Chinese environments is reviewed, especially with regard to the formation of low-Se environments. The occurrence, distribution, concentration and flux of Se in Chinese environments are reported in comparison to those in the rest of the world. Low-Se regions in China can be classified into 4 categories. In the NE, organic matter in the soil affects bioavailability of Se in soil. In the Huabei plain, the concentration of soil Se is strongly influenced by leaching and hydrological transport processes and Se deficient regions are mostly located on the hill-slopes due to leaching. In the Loessial Plateau, low-Se soils have developed on the low-Se parent material with a very low flux of Se between soil and plants. Low-Se regions in the SW have soils derived from weathered materials of lower Se contents. Both the lowest and highest concentrations and the flux of Se in environments are reported for China. #

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Some organochlorine pesticides (OCPs) are suspected of modulating the endocrine systems of humans. Aspects of neuro-endocrine system modulation include interactions such as agonism or antagonism of estrogen receptor (ER) binding. However, less is known about their interactions with other nuclear receptors (NRs). The objectives of this study were to determine and compare the ability of p,p'-dichlorodiphenylethane (p,p'-DDE), p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT), hexachlorobenzene (HCB) and r-hexachlorocyclohexane (r-HCH) to interact with ERalpha, androgen receptor (AR), progesterone receptor (PR) and estrogen-related receptor (ERRgamma) using a set of recombined yeast strains expressing beta-galactosidase, under control of ERalpha, AR, PR or ERRgamma. The results showed that p,p'-DDE was an ERalpha agonist, AR and PR antagonist (PR>AR), while p,p'-DDT was an ERalpha agonist and AR antagonist. HCB and r-HCH were antagonists for AR and ERRgamma, while r-HCH was a PR antagonist and a weak antagonist of ERRgamma, and was able to reverse the ERRgamma inhibition induced by 4-hydroxytamoxifen. All the results suggested that, for the tested OCPs, their ability to act as endocrine disruptors involves more than one mechanism, their (anti-)agonistic effects on different receptors should not be overlooked, and the potential for additive or synergistic effects must be taken into consideration in the risk assessment process.

In this paper, the movement behavior of Daphnia magna was studied as a bio-indicator of organophosphorous pesticide (OP) contamination, using an on-line bio-monitoring method, the Multispecies Freshwater Biomonitor®. A static test of acute toxicity test revealed the 24-h and 48-h LC 50 values (95% confidence limit) for Daphnia magna to be respectively 0.45 μg/l and 0.21 μg/l for dipterex 3.80 μg/l and 0.90 μg/l for malathion, and 1.25 μg/l and 0.38 μg/l for parathion. The behavior strength of Daphnia magna was a sensitive indicator of sublethal OP stress and resulted in significant concentrationresponse relationships for the three OPs. Increasing OP concentration will result in more intensive behavioral responses of Daphnia magna and shorter response time, which could be described by the Stepwise Stress Model (SSM). Therefore movement behavior can be effectively applied in early warning of environment quality by on-line bio-monitoring. The intensive changes in behavior strength of Daphnia magna over a short time follow the SSM concept and can be used as an indicator of early stress response to OP accidental contamination.

Sediment toxicity from hydrophobic organic compounds (HOCs) is complicated by chemical partitioning among multiple phases and sediment-specific bioavailability. In this study, we used three hydrophobic pyrethroid insecticides as test compounds and derived 10-d median lethal concentrations (LC50s) for Chironomus tentans in three different sediments. The LC50s were expressed using HOC concentrations on a bulk sediment basis (C(S)), organic carbon (OC)-normalized sediment basis (C(S-OC)), porewater basis (C(PW)), dissolved organic carbon (DOC)-normalized porewater basis (C(PW-DOC)), and freely dissolved porewater basis (C(free)). The bulk phase C(S) and C(PW) yielded highly variable LC50s across sediment types, whereas the use of normalized concentrations C(S-OC) and C(PW-DOC) generally reduced variability due to sediment type but not that due to aging. In contrast, LC50s based on C(free) were essentially independent of sediment conditions. The sediment pore water samples contained approximately 20-90 mg L(-1) DOC, and the C(free) expressed as a percentage of the total bulk pore water concentration ranged from 9 to 28% for fenpropathrin (mean = 19%), 8 to 18% for bifenthrin (mean = 13%), and 3 to 8% for cyfluthrin (mean = 6%) across the different sediments. These results indicate thatthe use of C(free) reduces uncertainties caused by sediment variables such as OC properties and aging effects.