Waterborne exposure to PFOS causes disruption of the hypothalamus-pituitary-thyroid axis in zebrafish larvae

Thyroid hormones (THs) play an important role in the normal development and physiological functions in fish. Environmental chemicals may adversely affect thyroid function by disturbing gene transcription. Perfluorooctane sulfonate (PFOS), a persistent compound, is widely distributed in the aquatic environment and wildlife. In the present study, we investigated whether PFOS could disrupt the hypothalamic-pituitary-thyroid (HPT) axis. Zebrafish embryos were exposed to various concentrations of PFOS (0, 100, 200 and 400 mu g L-1) and gene expression patterns were examined 15 d post-fertilization. The expression of several genes in the HIPT system, i.e., corticotropin-releasing factor (CRF), thyroid-stimulating hormone (TSH), sodium/iodide symporter (NIS), thyroglobulin (TG), thyroid peroxidase (TPO), transthyretin (TTR), ioclothyronine deiodinases (Dio1 and Dio2) and thyroid receptor (TR alpha and TR beta), was quantitatively measured using real-time PCR. The gene expression levels of CRF and TSH were significantly up-regulated and down-regulated, respectively, upon exposure to 200 and 400 mu g L-1 PFOS. A significant increase in NIS and Diol gene expression was observed at 200 mu g L-1 PFOS exposure, while TG gene expression was down-regulated at 200 and 400 mu g L-1 PFOS exposure. TTR gene expression was down-regulated in a concentration-dependent manner. Up-regulation and down-regulation of TR alpha and TR beta gene expression, respectively, was observed upon exposure to PFOS. The whole body thyroxine (T-4) content remained unchanged, whereas triiodothyronine (T-3) levels were significantly increased, which could directly reflect disrupted thyroid hormone status after PFOS exposure. The overall results indicated that PFOS exposure could alter gene expression in the HPT axis and that mechanisms of disruption of thyroid status by PFOS could occur at several steps in the synthesis, regulation, and action of thyroid hormones. (C) 2009 Elsevier Ltd. All rights reserved.

Reduction in microcystin concentrations in large and shallow lakes: Water and sediment-interface contributions

Blooms of cyanobacteria, or blue-greens, are known to produce chemicals, such as microcystins, which can be toxic to aquatic and terrestrial organisms. Although previous studies have examined the fate of microcystins in freshwater lakes, primary elimination pathways and factors affecting degradation and loss have not been fully explained. The goal of the present study was to explore sources of algal toxins and investigate the distribution and biodegradation of microcystins in water and sediment through laboratory and field analyses. Water and sediment samples were collected monthly from several locations in Lake Taihu from February 2005 to January 2006. Samples were analyzed for the presence of microcystin. Water and sediment were also used in laboratory studies to determine microcystin degradation rates by spiking environmental samples with known concentrations of the chemical and observing concentration changes over time. Some water samples were found to efficiently degrade microcystins. Microcystin concentrations dropped faster in water collected immediately above lake sediment (overlying water). Degradation in sediments was higher than in water. Based on spatial distribution analyses of microcystin in Lake Taihu, higher concentrations (relative to water concentrations) of the chemical were found in lake sediments. These data suggest that sediments play a critical role in microcystin degradation in aquatic systems. The relatively low levels of microcystins found in the environment are most likely due to bacterial biodegradation. Sediments play a crucial role as a source (to the water column) of bio-degrading bacteria and as a carbon-rich environment for bacteria to proliferate and metabolize microcystin and other biogenic toxins produced by cyanobacteria. These, and other, data provide important information that may be applied to management strategies for improvement of water quality in lakes, reservoirs and other water bodies. (C) 2007 Elsevier Ltd. All rights reserved.

The involvement of the antioxidant system in protection of desert cyanobacterium Nostoc sp against UV-B radiation and the effects of exogenous antioxidants

In this study, we found that UV-B radiation decreased photosynthetic activity and boosted lipid peroxidation of desert Nostoc sp., and exogenous chemicals (ascorbate acid (ASC), N-acetylcysteine (NAC), and sodium nitroprusside (SNP)) had obvious protective effects on photosynthesis and membranes under UV-B radiation. High-concentration SNP boosted the activities of antioxidant enzymes, but low-concentration SNP reduced the activities of antioxidant enzymes. Both NAC and ASC treatments of cells decreased activities of antioxidant enzymes. The results suggested that those chemicals possibly had different mechanisms of protection of algae cells against UV-B radiation. SNP might play double roles as a signal molecule in the formation of algae cell protection of Photosystem 11 under UV-B radiation and as a (reactive oxygen species) scavenger, while NAC and ASC might function as antioxidant reagents or precursors of other antioxidant molecules, which could protect cells directly against ROS initiated by UV-B radiation. (c) 2006 Elsevier Inc. All rights reserved.

Allelopathic interactions between Potamogelon maackianus and Microcystis aeruginosa

The allelopathic interactions between Potamogeton maackianus and toxic cyanobacteria (Microcystis aeruginosa) were studied. P maackianus inhibited the growth of M. aeruginosa, both in a coexistence culture system and in exudates experimental culture system. M. aeruginosa also showed effects on the secondary metabolic biosynthesis and secreting behavior of P maackianus. The main lipophilic components of the hexane extracts and the exudates from the macrophyte were analyzed through GC-MS determination. The lipophilic components of the hexane extracts and the exudates from P. maackianus were influenced by M. aeruginosa or their released chemicals. Comparing the lipophilic constituents of the hexane extracts with those in the exudates, the results showed that weak polar compounds contained in the macrophytes can be secreted into the surrounding water. Many compounds, such as N-phenyl-2-naphthalenamine and isopropyl myristate, were detected both in the hexane extracts and the exudates. The changes of lipophilic components in the hexane extracts would be a response to the stress of toxic cyanobacteria or their released toxins. Those changes of exudates, especially the increased content of N-phenyl-2-naphthalenamine, might also be an induced defensive behavior mediated by the released toxins from M aeruginosa. The study results about reciprocal allelopathic responses between macrophytes and cyanobacteria can help in the management of eutrophic waters, and is also important information concerning strategies for recovering eutrophic waters.

Prenatal exposures to persistent organic pollutants as measured in cord blood and meconium from three localities of Zhejiang, China

Prenatal exposures to persistent organic pollutants were assessed using the levels of PCBs and organochlorine pesticides (OCPs) measured in cord blood and meconium samples from Luqiao and two other localities of the Zhejiang province in China. Luqiao is a town with the largest site for disassembly of PCB-containing obsolete transformers and electrical waste in China. The other two localities Pingqiao (100 km NW of Luqiao) and Lin'an (500 km NW of Luqiao) are towns without known electronic or electrical waste sites. A total of 23 PCB congeners (including 12 dioxin-like) and 6 OCPs were measured using the traditional GC-mu ECD technique. Micro-EROD bioassay was additionally used to measure TCDD-based TEQ levels of the 12 dioxin-like PCBs. Significant correlations were found between the TEQs measured by the two methods, supporting the application of micro-EROD as a practical toot for complementing the chemical analysis. The data showed that beta-HCH, p,p'-DDE, and 6 PCB congeners (101, 138 153, 180, 183, and 187) were the predominant pollutants, with PCB 138 being the best indicator (predictor) for total PCB levels. Cord blood and meconium from Luqiao have higher levels of PCBs than those from the other two localities, suggesting that a disassembly site for electronic and electric waste would provide an environment for greater exposure to these chemicals. The cord blood or meconium levels of beta-HCH, though likewise considerably high, were comparable in the three localities. Similar findings were observed for p,p'-DDE. Pollution by these OCPs might have come from past use of agricultural pesticides in the three localities. (c) 2007 Published by Elsevier B.V.

Effects of brominated flame retardants and brominated dioxins on steroidogenesis in H295R human adrenocortical carcinoma cell line

Brominated flame retardants (BFRs) and brominated dioxins are emerging persistent organic pollutants that are ubiquitous in the environment and can be accumulated by wildlife and humans. These chemicals can disturb endocrine function. Recent studies have demonstrated that one of the mechanisms of endocrine disruption by chemicals is modulation of steroidogenic gene expression or enzyme activities. In this study, an in vitro assay based on the H295R human adrenocortical carcinoma cell line, which possesses most key genes or enzymes involved in steroidogenesis, was used to examine the effects of five bromophenols, two polybrominated biphenyls (PBBs 77 and 169), 2,3,7,8-tetrabromodibenzo-p-dioxin, and 2,3,7,8-tetrabromodibenzofuran on the expression of 10 key steroidogenic genes. The H295R cells were exposed to various BFR concentrations for 48 h, and the expression of specific genescytochrome P450 (CYP11A, CYP11B2, CYP17, CYP19, and CYP21), 3 beta-hydroxysteroid dehydrogenase (3PHSD2), 17 beta-hydroxysteroid dehydrogenase (17 beta HSD1 and 17 beta HSD4), steroidogenic acute regulatory protein (StAR), and 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR)-was quantitatively measured using real-time polymerase chain reaction. Cell viability was not affected at the doses tested. Most of the genes were either up- or down-regulated, to some extent, by BFR exposure. Among the genes tested, 3PHSD2 was the most markedly up-regulated, with a range of magnitude from 1.6- to 20-fold. The results demonstrate that bromophenol, bromobiphenyls, and bromodibenzo-p-dioxin/furan are able to modulate steroidogenic gene expression, which may lead to endocrine disruption.

Primary cultured cells as sensitive in vitro model for assessment of toxicants-comparison to hepatocytes and gill epithelia

In an effort to develop cultured cell models for toxicity screening and environmental biomonitoring, we compared primary cultured gill epithelia and hepatocytes from freshwater tilapia (Oreochromis niloticus) to assess their sensitivity to AhR agonist toxicants. Epithelia were cultured on permeable supports (terephthalate membranes, "filters") and bathed on the apical with waterborne toxicants (pseudo in vivo asymmetrical culture conditions). Hepatocytes were cultured in multi-well plates and exposed to toxicants in culture medium. Cytochrome P4501A (measured as 7-Ethoxyresorufin-O-deethylase, EROD) was selected as a biomarker. For cultured gill epithelia, the integrity of the epithelia remained unchanged on exposure to model toxicants, such as 1,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), benzo(a)pyrene B[a]P, polychlorinated biphenyl (PCB) mixture (Aroclor 1254), and polybrominated diphenyl ether (PBDE) mixture (DE71). A good concentration-dependent response of EROD activity was clearly observed in both cultured gill epithelia and hepatocytes. The time-course response of EROD was measured as early as 3 h, and was maximal after 6 h of exposure to TCDD, B [alp and Aroclor 1254. The estimated 6 h EC50 for TCDD, B [a]P, and Aroclor 1254 was 1.2x10(-9), 5.7x10(-8) and 6.6x10(-6) M. For the cultured hepatocytes, time-course study showed that a significant induction of EROD took place at 18 h, and the maximal induction of EROD was observed at 24 h after exposure. The estimated 24 It EC50 for TCDD, B[a]P, and Aroclor 1254 was 1.4x10(-9), 8.1x10(-8) and 7.3x10(-6) M. There was no induction or inhibition of EROD in DE71 exposure to both gill epithelia and hepatocytes. The results show that cultured gill epithelia more rapidly induce EROD and are slightly more sensitive than cultured hepatocytes, and could be used as a rapid and sensitive tool for screening chemicals and monitoring environmental AhR agonist toxicants. (c) 2006 Elsevier B.V. All rights reserved.

A screening study on persistent bioaccumulation toxins (PBT) in fuel combustion soot

Persistent bioaccumulative toxins (PBTs) are organic substances that are persistent, bioaccumulative and can cause severe toxic effects (e.g. potential oncogens, mutagenic, endocrine disrupters) to human health or environment which are the ones that need special attention. PBT chemicals could be released to the environment from several types of sources and are ubiquitous in environment. However, fast and efficiency monitoring and assessment methods to investigate PBTs in environment are still lacking. In this study, a cleaning-up procedure of analyzing PBTs in fuels combustion soot was developed and its performance was assessed through comparing the chromatograms of crude extracts with their cleaned extracts after the cleaning-up procedure. The results showed that polycyclic aromatic compounds (PACs) were the main components in fuel combustion soot and the clean-up procedure developed in this paper can be well used as the method of analyzing PBTs in fuels combustion soot.

Reproductive effects of prenatal exposure to nonylphenol on zebrafish (Danio rerio)

Mature female and male zebrafish were separated and exposed to nonylphenol (NP) at 0.1, 1, 10, 50, 100 and 500 mu g/L, respectively, for 3 weeks. Gonadosomatic index (GSI) in both sexes and vitellogenin (VTG) induction in males was measured as the bioindicators for the impairment to the parents. The results indicated that 50 mu g/L of NP was the non-observed effect concentration (NOEC) for GSI and VTG induction. Afterwards, the 50 mu g/L NP exposed females and males, and the control females and males were cross-wise pair-bred in the control water for one week to examine the reproductive effects. The embryonic cathepsin D (CAT D) activity, eggshell thickness, fecundity, hatching rate and malformation (vertebral column flexure) rate of offspring were determined in the four pair-bred groups. While endpoints remained unchanged in the groups with exposed males, prenatal exposure of females to 50 mu g/L of NP resulted in the impairment of reproduction in groups with exposed females including inhibition of CAT D activity (P < 0.05), decrease of eggshell thickness (by 23.6%) and elevation of malformation rate (P < 0.001). These results suggested NP could induce reproductive damage to zebrafish at NOEC for parents. The results also imply that alterations of CAT D activity and eggshell thickness may be more sensitive biomarkers to indicate the reproductive effects caused by endocrine disrupting chemicals. (c) 2005 Elsevier Inc. All rights is reserved.

Assessment of estrogenic activity of leachate from automobile tires with two in vitro bioassays

In this study, a combination of enzyme-linked receptor assay (ELRA) and yeast estrogen screen (YES) assay was firstly applied to determine whether automobile tires immersed in fresh water can leach chemicals, which display estrogenic activity. We optimized ELRA substituting the chromogene substrate by a luminescent one, and found that luminescent ELBA was more sensitive to 17 beta-estradiol (17 beta-E2) with a detection limit of 0.016 mu g/l, compared to 0.088 mu g/l in the chromogene version. In ELRA, all tire leachates obviously showed estrogenic activity, which was increased with duration of immersion. Moreover, the leachate from hackled tires showed more potent estrogenicity than that from the whole ones. In comparison to ELRA, no detectable estrogenic activity was found in all tire leachates with YES assay. The results from YES assay further evidenced that antiestrogenic compounds can be leached from tires. As tire leachates contain estrogenic compounds, they could be important pollution sources, potentially harmful to wildlife and human health. Thus, use of shredded tires as road fill or in landfill sites should arouse our attention.

Environmental signals: Synthetic humic substances act as xeno-estrogen and affect the thyroid system of Xenopus laevis

According to outdated paradigms humic substances (HS) are considered to be refractory or inert that do not directly interact with aquatic organisms. However, they are taken up and induce biotransformation activities and may act as hormone-like substances. In the present study, we tested whether HS can interfere with endocrine regulation in the amphibian Xenopus laevis. In order to exclude contamination with phyto-hormones, which may occur in environmental isolates, the artificial HS 1500 was applied. The in vivo results showed that HS 1500 causes significant estrogenic effects on X. laevis during its larval development and results of semi-quantitative RT-PCR revealed a marked increase of the estrogenic biomarker estrogen receptor mRNA (ER-mRNA). Furthermore, preliminary RT-PCR results showed that the thyroid-stimulating hormone (TSH beta-mRNA) is enhanced after exposure to HS1500, indicating a weak adverse effect on T3/T4 availability. Hence, HS may have estrogenic and anti-thyroidal effects on aquatic animals, and therefore may influence the structure of aquatic communities and they may be considered environmental signaling chemicals. (c) 2005 Elsevier Ltd. All rights reserved.

Effects of polyaluminum chloride and copper sulfate on phosphorus and UV254 under different anoxic levels

Experimental sediments and water from shallow, eutrophic Dianchi Lakes were treated in a controlled laboratory microcosm using different chemicals under different anoxic levels. This study revealed that the polyaluminum chloride (PAC) was able to inhibit the phosphorus release and decrease the UV254 value at any anoxic level. When the DO concentrations were between 0.76-0.95 mg(.) L-1, the UV(254)value, total phosphorus (TP), and total dissolved phosphorus (TDP) in the water column were decreased by 71.93%, 87.12% and 64.24% respectively. The UV254, TP, and TDP were also decreased by 72.94%, 70.87% and 50.76% respectively at the levels of 4.56-5.32mg(.)L(-1) of DO concentrations. The treatment effects of TP and TDP in the water column using copper sulfate however were not as efficient as the PAC treatment. The UV254 value was increased with the addition of copper sulfate at every anoxic level tested but the chlorophyll-a (Chl-a) content was decreased rapidly and efficiently by copper sulfate more than the treatment by PAC. When the DO concentrations were 0.76-0.86mg(.)L(-1) and 4.75-5.14mg(.)L(-1), the Chl-a concentrations were decreased by 84.87% and 75.07% respectively through copper sulfate treatment. With additions of PAC and copper sulfate, the phosphorus fractions in sediments were shifted forward to the favorable shapes that have little ability of release. The TP concentrations in sediments were increased after treatment via PAC and copper sulfate. Under anoxic conditions, most of the BD-P (Fe-P) to NaOH-P (Al-P) was converted using the recommended PAC dose in BD-P rich sediment. Similar to the PAC, the copper sulfate also could flocculate the exchange phosphorus from sediment to overlying water. Overall though, the effects of copper sulfate treatment were not better than that of the PAC.

The Chinese rare minnow (Gobiocypris rarus) as an in vivo model for endocrine disruption in freshwater teleosts: a full life-cycle test with diethylstilbestrol

Chinese rare minnow (Gobiocypris rarus), a freshwater teleost,. was exposed to diethylstilbestrol (DES) at 0.05, 0.5, 1 and 5 mug/L from fertilized eggs for up to mature period under flow-through condition. Several endpoints that related to development, reproductive fitness and transgenerational effects were evaluated. It was found that body length and body weight were significantly reduced and vitellogenin (Via) levels were significantly increased for fish exposed to DES. Histological examination showed that the sex ratios of F-0 fish skewed to female and about 2% of the fish exposed to 0.05 mug/L DES developed testes-ova. The reproductive success, as determined from data on egg production, was reduced in female fish exposed to 0.05, 0.5, 1 and 5 mug/L DES. The lowest-observed-effect concentrations (LOEC) for chances of sex ratios, reproductive success and histology alteration of F-0 are 0.05 mug/L. In the offspring, transgenerational effects on egg hatching rate. egg fertilization and Vtg levels of juvenile individuals were not observed. However. survival of F, generation fry significantly declined. The analysis of sex steroid levels revealed a significant decrease of testosterone (T) in the whole body homogenates (WBH) of male progeny and somewhat elevation of estradiol (E-T) in the WBH of female offspring. These findings indicate that exposure to DES causes a variety of developmental, reproductive and transgenerational effects. (C) 2004 Elsevier B.V. All rights reserved.

Effects of nitrogen forms on the production of cyanobacterial toxin microcystin-LR by an isolated Microcystis aeruginosa

A cyanobacterial strain, which produced high content of microcystin-LR (MC-LR) but no rnicrocystin-RR (MC-RR), was isolated from the hypertrophic Dianchi Lake in China and identified as Microcystis aeruginosa DC-1. Effects of nitrogen containing chemicals and trace elements on the growth and the production of MC-LR by this strain were Studied. In the presence of bicine, compared with urea and ammonium, nitrate greatly promoted the growth and the production of MC-LR. However, leucine and arginine, which were the constitutional components in the molecular structure of MC-LR or RR, inhibited the production of MC-LR. Iron and silicon up to 10mg/L had little effects on the growth of M. aeruginosa DC-1, but the production of MC-LR was apparently enhanced. Under all conditions studied here, only MC-LR but no RR was detected within the cells of M. aeruginosa DC-1. Thus, chemical forms of nitrogen, rather than the usually concerned the total nitrogen, Lind trace elements played important roles in the production of MC toxins during cyanobacterial blooms.