Chronic Methylmercury Exposure Induces Production of Prostaglandins: Evidence From A Population Study and A Rat Dosing Experiment.

Methylmercury (MeHg) is a well-known environmental neurotoxicant affecting millions worldwide who consume contaminated fishes and other food commodities. Exposure to MeHg has been shown to associate positively with some chronic diseases including cardiovascular diseases, but the mechanism is poorly characterized. MeHg had been shown to affect prostaglandin (PG) regulations in in vitro studies, but neither in vivo nor human studies investigating the effects of MeHg on PG regulations has been reported. Thus, the current study aimed to investigate the association between MeHg exposure and serum PG concentrations in a cross-sectional study among human adults followed by a validation investigation on the cause-effect relationship using a rat model. First, a total of 121 women were recruited from two cities: Wanshan and Leishan in Guizhou, China. Statistical analysis of the human data showed a positive association between blood total mercury (THg) levels and serum concentrations of PGF2α, 15-deoxy-PGJ2, and PGE2 after adjusting for site effects. In the animal study, adult female Sprague-Dawley rats were dosed with 40 µg MeHg/kg body weight/day for 12 weeks. Serum 15-deoxy-PGJ2 and 2,3 d-6-keto-PGF1α concentrations were found to increase significantly after 6 and 10 weeks of MeHg dosing, respectively, while serum PGF2α concentration increased significantly after 12 weeks of MeHg dosing. Combined results of our human and rat studies have shown that chronic MeHg exposure induced dysregulation of PG metabolism. As PGs are a set of mediators with very diverse functions, its abnormal production may serve as the missing mechanistic link between chronic MeHg exposure and various kinds of associated clinical conditions including neurodegeneration and cardiovascular diseases.

Temperature-dependent physiological and biochemical responses of the marine medaka Oryzias melastigma with consideration of both low and high thermal extremes.

This study aimed to investigate temperature effect on physiological and biochemical responses of the marine medaka Oryzias melastigma larvae. The fish were subjected to a stepwise temperature change at a rate of 1 °C/h increasing or decreasing from 25 °C (the control) to six target temperatures (12, 13, 15, 20, 28 and 32 °C) respectively, followed by a 7-day thermal acclimation at each target temperature. The fish were fed ad libitum during the experiment. The results showed that cumulative mortalities were significantly increased at low temperatures (12 and 13 °C) and at the highest temperature (32 °C). For the survivors, their growth profile closely followed the left-skewed 'thermal performance curve'. Routine oxygen consumption rates of fish larvae were significantly elevated at 32 °C but suppressed at 13 and 15 °C (due to a high mortality, larvae from 12 °C were not examined). Levels of heat shock proteins and activities of malate dehydrogenase and lactate dehydrogenase were also measured in fish larvae exposed at 15, 25 and 32 °C. The activities of both enzymes were significantly increased at both 15 and 32 °C, where the fish larvae probably suffered from thermal discomfort and increased anaerobic components so as to compensate the mismatch of energy demand and supply at these thermal extremes. Coincidently, heat shock proteins were also up-regulated at both 15 and 32 °C, enabling cellular protection. Moreover, the critical thermal maxima and minima of fish larvae increased significantly with increasing acclimation temperature, implying that the fish could develop some degrees of thermal tolerance through temperature acclimation.

Extreme cold or warm events can potentially exacerbate chemical toxicity to the marine medaka fish Oryzias melastigma.

Marine ecosystems are currently subjected to dual stresses of chemical pollution and climate change. Through a series of laboratory experiments, this study investigated the impact of exposure to chemical contaminant such as DDT or copper (Cu), in combination with cold or warm temperature extremes on the marine medaka fish Oryzias melastigma. The results showed that extreme seawater temperatures (i.e., 15 and 32 °C in sub-tropical Hong Kong) exacerbated adverse chemical impacts on the growth performance of O. melastigma, in particular at the high thermal extreme. This was likely associated with an interruption of oxygen consumption and aerobic scope. Most importantly, the results of acclimation experiments, as reflected by thermal tolerance polygons, showed that chemical exposure substantially narrowed the thermal tolerance of the medaka, making them more vulnerable to temperature changes and extreme thermal events. Under dual stresses of thermal extremes and chemical exposure, the medaka switched their metabolic pathway to anaerobic respiration that might deplete their energy reserve for chemical detoxification. Although stress proteins such as heat shock proteins (HSP90) were up-regulated for cellular protection in the fish, such a defensive mechanism was repressed with intensifying dual stresses at high temperature and high chemical concentration. Bioconcentration of DDT or Cu generally increased with increasing temperature and its exposure concentration. Overall, these complex chemical-temperature interactions concomitantly exerted a concerted adverse impact to O. melastigma. The temperature-dependent toxicity of DDT or Cu shown in this study clearly demonstrated the potential challenge brought by the risk of chemical pollution under the impact of global climate change.

Seasonal Growth of the Purple Sea Urchin Heliocidaris crassispina Revealed by Sequential Fluorochrome Tagging.

Many studies have applied fluorochrome tagging to examine the growth of animals with calcified skeletons, but most of them have used only a single tag to determine the annual growth rate. We used sequential fluorochrome tagging to study the seasonal growth of the purple sea urchin Heliocidaris crassispina in Hong Kong waters from February 2012 to February 2013. Sea urchins ranging from 18.9 to 42.7 mm in test diameter had a yearly growth from 0.6 to 13.0 mm. During that year, the sea urchins grew from 0.6 to 5.0 mm in test diameter during the first six months, and from 0.4 to 10.2 mm in test diameter in the second six months. The seasonal differences in growth were confirmed using the von Bertalanffy model. The growth was clear for young sea urchins, especially for individuals less than 5 years old, but was not evident for sea urchins older than 7 years. The seasonal differences in growth were probably related to the reproductive cycle and the seasonal differences in environmental conditions. Our empirical results provide the first evidence of seasonal changes in growth for H. crassispina, demonstrating the usefulness of sequential fluorochrome tagging in studying the growth of sea urchins in the field. We also identify the problem of low recovery of tagged individuals and provide recommendations to improve the tagging procedure.

Thermal extremes can intensify chemical toxicity to freshwater organisms and hence exacerbate their impact to the biological community.

Temperature in freshwater ecosystems fluctuates daily, seasonally and yearly. Climate change further induces temperature variations. In this study, we hypothesise that water temperatures, in particular thermal extremes, can significantly influence chemical toxicity to ectothermic organisms. Although temperature-dependent chemical toxicity (TDCT) is a classic research area in ecotoxicology, a unified model for predicting TDCT for freshwater species is yet to be developed. This study aimed to address this challenging issue through a meta-analysis by comparing acute toxicity endpoints (i.e. median lethal or effective concentration data; LC50 or EC50) of 13 chemicals for various freshwater species generated from different temperatures. Our results suggest that in most cases, freshwater species exhibit the highest tolerance towards chemicals at their physical optimal temperature (Topt), and chemical toxicity exacerbates when temperature is higher or lower than Topt (i.e. inverted V-shaped model between temperature and LC50 or EC50). Such observations are further supported by temperature-dependent hazardous concentration 10% (HC10) values derived from species sensitivity distributions constructed using toxicity data generated at different temperatures. A unified mathematical model was also developed to describe the inverted V-shape relationship between temperature and HC10 derivations. Overall, considering the natural variations of freshwater temperatures, the inverted V-shaped TDCT model can be readily applied to derive water quality guidelines and assess ecological risks of chemical contaminants.

Deriving site-specific sediment quality guidelines for Hong Kong marine environments using field-based species sensitivity distributions.

Field data of benthic communities and contaminant loadings in marine sediments measured in parallel can be used to derive sediment quality guidelines (SQGs) using a field-based species sensitivity distribution (f-SSD) approach. Recently, SQGs have been successfully derived from f-SSDs for the Norwegian continental shelf with an extensive survey (>1 million km(2)) and a large data set (1,902 sampling stations with 1,944 species). The present study examined the practicality of this approach in deriving SQGs for a much smaller geographical area, namely, the marine environment of Hong Kong (sea area: 1,651 km(2)), making use of databases of the government of Hong Kong special administrative region. As the construction of f-SSDs requires the use of a collection of responses from individual species to a chemical gradient in sediment, data screening criteria on the minimum abundance of the species were evaluated and optimized to ensure sufficient statistical power for estimating these responses. Sediment quality guidelines were derived for nine trace metals, total polycyclic aromatic hydrocarbons, and total polychlorinated biphenyls and compared with current SQGs in developed countries. The community-adjusted hazardous concentrations of 5% and 10% of the f-SSDs were adopted to represent the threshold effects level (TEL) and predicted effects level (PEL), respectively. The TELs derived from this f-SSD approach compares favorably with current SQGs, while the derived PELs were generally lower than the current SQGs, indicating that they are more protective. The f-SSDs can be directly utilized for probabilistic risk assessment, while the field-based SQGs can be used as site-specific guidelines or integrated into current SQGs. Our results suggest that the f-SSD approach can also be applicable to small areas such as Hong Kong.

Synergistic toxic effects of zinc pyrithione and copper to three marine species: Implications on setting appropriate water quality criteria.

Zinc pyrithione (ZnPT) is widely applied in conjunction with copper (Cu) in antifouling paints as a substitute for tributyltin. The combined effects of ZnPT and Cu on marine organisms, however, have not been fully investigated. This study examined the toxicities of ZnPT alone and in combination with Cu to the diatom Thalassiosira pseudonana, polychaete larvae Hydroides elegans and amphipod Elasmopus rapax. Importantly, ZnPT and Cu resulted in a strong synergistic effect with isobologram interaction parameter lambda>1 for all test species. The combined toxicity of ZnPT and Cu was successfully modelled using the non-parametric response surface and its contour. Such synergistic effects may be partly due to the formation of copper pyrithione. It is, therefore, inadequate to assess the ecological risk of ZnPT to marine organisms solely based on the toxicity data generated from the biocide alone. To better protect precious marine resources, it is advocated to develop appropriate water quality criteria for ZnPT with the consideration of its compelling synergistic effects with Cu at environmentally realistic concentrations.

Acute and chronic toxicities of zinc pyrithione alone and in combination with copper to the marine copepod Tigriopus japonicus.

Zinc pyrithione (ZnPT) is a widely used booster biocide in combination with copper (Cu) in antifouling paints as a substitute for tributyltin. The co-occurrence of ZnPT and Cu in coastal marine environments is therefore very common, and may pose a higher risk to marine organisms if they can result in synergistic toxicity. This study comprehensively investigated the combined toxicity of ZnPT and Cu, on the marine copepod Tigriopus japonicus, for the first time, based on both 96-h acute toxicity tests using adult copepods and chronic full-life cycle tests (21 d) using nauplii <24-h old. As ZnPT has been reported to be easily trans-chelated to copper pyrithione (CuPT) in the presence of Cu, the acute toxicities of CuPT alone and in combination with Cu on adult copepods were also assessed. Our results showed that ZnPT and Cu exhibited a strong synergistic toxic effect on the copepod in both acute and chronic tests. During the acute test, the mortalities of adult copepods increased dramatically even with an addition of Cu at concentrations as low as 1-2 µg/L compared with those exposed to ZnPT alone. Severe chronic toxicities were further observed in the copepods exposed to ZnPT-Cu mixtures, including a significant increase of naupliar mortality, postponing of development from naupliar to copepodid and from copepodid to adult stage, and a significant decrease of intrinsic population growth when compared with those of copepods exposed to ZnPT or Cu alone. Such synergistic effects might be partly attributable to the formation of CuPT by the trans-chelation of ZnPT and Cu, because CuPT was found to be more toxic than ZnPT based on the acute toxicity results. Mixtures of CuPT and Cu also led to synergistic toxic effects to the copepod, in particular at high Cu concentrations. A novel non-parametric response surface model was applied and it proved to be a powerful method for analysing and predicting the acute binary mixture toxicities of the booster biocides (i.e., ZnPT and CuPT) and Cu on the copepod. To better protect precious marine resources, it is necessary to revise and tighten existing water quality criteria for biocides, such as ZnPT and CuPT, to account for their synergistic effects with Cu at environmentally realistic levels.

Deriving field-based sediment quality guidelines from the relationship between species density and contaminant level using a novel nonparametric empirical Bayesian approach.

This paper describes a novel statistical approach to derive ecologically relevant sediment quality guidelines (SQGs) from field data using a nonparametric empirical Bayesian method (NEBM). We made use of the Norwegian Oil Industrial Association database and extracted concurrently obtained data on species density and contaminant levels in sediment samples collected between 1996 and 2001. In brief, effect concentrations (ECs) of each installation (i.e., oil platform) at a given reduction in species density were firstly derived by fitting a logistic-type regression function to the relationship between the species density and the corresponding concentration of a chemical of concern. The estimated ECs were further improved by the NEBM which incorporated information from other installations. The distribution of these improved ECs from all installations was determined nonparametrically by the kernel method, and then used to determine the hazardous concentration (HC) which can be directly linked to the species loss (or the species being protected) in the sediment. This method also enables an accurate estimation of the lower confidence limit of the HC, even when the number of observations was small. To illustrate the effectiveness of this novel technique, barium, cadmium, chromium, copper, mercury, lead, tetrahydrocannabinol, and zinc were chosen as example contaminants. This novel approach can generate ecologically sound SQGs for environmental risk assessment and cost-effectiveness analysis in sediment remediation or mud disposal projects, since sediment quality is closely linked to species density.

The difference between temperate and tropical saltwater species' acute sensitivity to chemicals is relatively small.

Due to a lack of saltwater toxicity data in tropical regions, toxicity data generated from temperate or cold water species endemic to North America and Europe are often adopted to derive water quality guidelines (WQG) for protecting tropical saltwater species. If chemical toxicity to most saltwater organisms increases with water temperature, the use of temperate species data and associated WQG may result in under-protection to tropical species. Given the differences in species composition and environmental attributes between tropical and temperate saltwater ecosystems, there are conceivable uncertainties in such 'temperate-to-tropic' extrapolations. This study aims to compare temperate and tropical saltwater species' acute sensitivity to 11 chemicals through a comprehensive meta-analysis, by comparing species sensitivity distributions (SSDs) between the two groups. A 10 percentile hazardous concentration (HC10) is derived from each SSD, and then a temperate-to-tropic HC10 ratio is computed for each chemical. Our results demonstrate that temperate and tropical saltwater species display significantly different sensitivity towards all test chemicals except cadmium, although such differences are small with the HC10 ratios ranging from 0.094 (un-ionised ammonia) to 2.190 (pentachlorophenol) only. Temperate species are more sensitive to un-ionised ammonia, chromium, lead, nickel and tributyltin, whereas tropical species are more sensitive to copper, mercury, zinc, phenol and pentachlorophenol. Through comparison of a limited number of taxon-specific SSDs, we observe that there is a general decline in chemical sensitivity from algae to crustaceans, molluscs and then fishes. Following a statistical analysis of the results, we recommend an extrapolation factor of two for deriving tropical WQG from temperate information.

Acute and chronic toxicities of Irgarol alone and in combination with copper to the marine copepod Tigriopus japonicus.

Irgarol 1051 has been widely used as a booster biocide in combination with copper (Cu) in antifouling paints. The combined toxicity of Irgarol with Cu on marine organisms, however, has not been fully investigated. This study investigated the acute and chronic toxicities of binary mixtures of Irgarol and CuSO(4) to the marine copepod Tigriopus japonicus. The acute combined toxicity of Irgarol and Cu was simple additive as revealed by two response surface models and their contours. However, based on chronic full life-cycle tests, when Irgarol was combined with Cu at an environmentally realistic concentration (10 µg L(-1)), a slightly synergistic effect was observed at a high Irgarol concentration (940 µg L(-1)), as shown by a significant increase in larval mortality. As Cu contamination is widespread in coastal environments, our results entail the importance of considering the combined toxic effect of the booster biocide and Cu for setting ecologically realistic water quality criteria.

Use of field data to support European Water Framework Directive quality standards for dissolved metals.

Quality standards (QS) for dissolved metals in freshwaters have been proposed underthe European Water Framework Directive (WFD) and are based mainly upon laboratory ecotoxicity data. Uncertainties remain about laboratory-to-field extrapolation to establish QS that are neither over- nor underprotective. Freshwater benthic macroinvertebrates are a group of organisms of known sensitivity to heavy metals. We analyzed a dataset from England and Wales of dissolved metal concentrations (cadmium, chromium, copper, iron, nickel, lead, and zinc) and associated benthic invertebrate community metrics, using piecewise regression, quantile regression, and information on metal concentrations consistent with good quality status. Analysis of these field data suggests that dissolved metal QS proposed under the WFD are similar to metal concentrations in rivers associated with unimpaired benthic invertebrate assemblages in England and Wales. The only exceptions to this are QS for iron and zinc, where use of relatively large assessment factors leads to standards that are substantially below concentrations associated with impaired invertebrate assemblages in the field.

Comparison of tropical and temperate freshwater animal species' acute sensitivities to chemicals: implications for deriving safe extrapolation factors.

Toxicity data for tropical species are often lacking for ecological risk assessment. Consequently, tropical and subtropical countries use water quality criteria (WQC) derived from temperate species (e.g., United States, Canada, or Europe) to assess ecological risks in their aquatic systems, leaving an unknown margin of uncertainty. To address this issue, we use species sensitivity distributions of freshwater animal species to determine whether temperate datasets are adequately protective of tropical species assemblages for 18 chemical substances. The results indicate that the relative sensitivities of tropical and temperate species are noticeably different for some of these chemicals. For most metals, temperate species tend to be more sensitive than their tropical counterparts. However, for un-ionized ammonia, phenol, and some pesticides (e.g., chlorpyrifos), tropical species are probably more sensitive. On the basis of the results from objective comparisons of the ratio between temperate and tropical hazardous concentration values for 10% of species, or the 90% protection level, we recommend that an extrapolation factor of 10 should be applied when such surrogate temperate WQCs are used for tropical or subtropical regions and a priori knowledge on the sensitivity of tropical species is very limited or not available.

Deriving sediment quality guidelines from field-based species sensitivity distributions.

The determination of predicted no-effect concentrations (PNECs) and sediment quality guidelines (SQGs) of toxic chemicals in marine sediment is extremely important in ecological risk assessment. However, current methods of deriving sediment PNECs or threshold effect levels (TELs) are primarily based on laboratory ecotoxicity bioassays that may not be ecologically and environmentally relevant. This study explores the possibility of utilizing field data of benthic communities and contaminant loadings concurrently measured in sediment samples collected from the Norwegian continental shelf to derive SQGs. This unique dataset contains abundance data for ca. 2200 benthic species measured at over 4200 sampling stations, along with co-occurring concentration data for >25 chemical species. Using barium, cadmium, and total polycyclic aromatic hydrocarbons (PAHs) as examples, this paper describes a novel approach that makes use of the above data set for constructing field-based species sensitivity distributions (f-SSDs). Field-based SQGs are then derived based on the f-SSDs and HCx values [hazardous concentration for x% of species or the (100-x)% protection level] by the nonparametric bootstrap method. Our results for Cd and total PAHs indicate that there are some discrepancies between the SQGs currently in use in various countries and our field-data-derived SQGs. The field-data-derived criteria appear to be more environmentally relevant and realistic. Here, we suggest that the f-SSDs can be directly used as benchmarks for probabilistic risk assessment, while the field-data-derived SQGs can be used as site-specific guidelines or integrated into current SQGs.