Acute effects of cadmium and copper on survival, oxygen consumption, ammonia-N excretion, and metal accumulation in juvenile Exopalaemon carinicauda

Chronic Cadmium Exposure can Alter Energy Allocation to Physiological Functions in the Shrimp Penaeus vannamei

Environmental stressors in aquatic organisms can be assessed using a bioenergetic approach based on the evaluation of changes in their physiological parameters. We evaluated the chronic effects of cadmium (Cd2+) on the energy balance as well as the survival, growth, metabolism, nitrogen excretion, hepatosomatic index, oxidized energy substrate, and osmoregulation of the shrimp Penaeus vannamei with the hypothesis that the high energy demand related to the homeostatic regulation of Cd2+could disrupt the energy balance and as a consequence, their physiological functions. The shrimp exposed to Cd2+ had higher mortality (30%), directed more energy into growth (33% of energy intake), ingested 10% more energy, and defecated less than control animals. Cd2+ exposure caused a tendency to decrease metabolism and ammonia excretion but did not alter the hepatosomatic index, type of energy substrate oxidized, and the hyperosmorregulatory pattern of the species. The Cd+2 exposure may have induced a trade-off response because there was a growth rate increase accompanied by increased mortality.

A review on sea cucumber (Bengali: Somuddro Sosha) as a bioindicator of heavy metal contamination and toxicity

This review paper exhibits the underexplored realm of heavy metal contamination and associated risks in sea cucumbers (SCs), which hold significant importance in traditional Asian marine diets and are globally harvested for the Asian market. The assessment focuses on heavy metals (HMs) presence in various SC species, revealing a global trend in HMs concentrations across anatomical parts: Fe > Zn > As > Cu > Hg > Pb > Mn > Cr > Ni > Cd. Specific species, such as Eupentacta fraudatrix, Holothuria mammata, Holothuria polii, Holothuria tubulosa, and Holothuria atra, exhibit heightened arsenic levels, while Stichopus herrmanni raises concerns with mercury levels, notably reaching 3.75 mg/kg in some instances, posing potential risks, particularly for children. The study sheds light on anthropogenic activities such as cultivation, fishing, and shipping, releasing HMs into marine ecosystems and thereby threatening ocean and coastal environments due to the accumulation and toxicity of these elements. In response to these findings, the paper suggests SCs as promising bioindicator species for assessing metal pollution in marine environments. It underscores the adverse effects of human actions on sediment composition and advocates for ongoing monitoring efforts both at sea and along coastlines.

Toxic effects of nanopolystyrene and cadmium on the intestinal tract of the Chinese mitten crab (Eriocheir sinensis)

Nanopolystyrene (NP) and cadmium (Cd) are ubiquitous contaminants in aquatic systems. The present study aimed to investigate the toxic effects of exposure to ambient concentrations of NP and/or Cd on the intestinal tract of the Chinese mitten crab (Eriocheir sinensis). Exposure to NP and/or Cd induced oxidative stress, as evidenced by a significant increase in lipid peroxide content (LPO), total antioxidant capacity (T-AOC), and peroxidase activity (POD), and significant decreases in superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX) activities in E. sinensis. In addition, exposure to NP and/or Cd imbalanced the homeostasis of the intestinal microbiota, as demonstrated by the significantly increased abundance of Spiroplasma. Transcriptomic and metabolomic analyses were performed to investigate the mechanisms underlying intestinal toxicity. Our results showed that ferroptosis, ABC transporters, phosphotransferase system, apoptosis, and leukocyte transendothelial migration were disturbed after exposure to NP and/or Cd. In particular, Cd exposure affected mucin type O-glycan biosynthesis, purine metabolism, and neuroactive ligand-receptor interaction. Intriguingly, co-exposure to NP and Cd might mitigate intestinal toxicity by decreasing oxidative stress and affecting these pathways. Taken together, our study clearly demonstrates that exposure to NP and/or Cd at environmentally relevant concentrations causes intestinal toxicity in E. sinensis.

Effects of copper on gill function of juvenile oriental river prawn (Macrobrachium nipponense): Stress and toxic mechanism

As an important trace element and the accessory factor of many enzymatic processes, heavy metal copper is essential to aquatic animals. The toxic mechanism of copper on gill function of M. nipponense was clarified for the first time in terms of histopathological analysis, physiology, biochemistry and the expression of important genes. The results obtained by present in present research showed that heavy metal copper could affect normal respiratory and metabolic activities in M. nipponense. Copper stress could cause damage to the mitochondrial membrane of gill cells in M. nipponense, and the activity of mitochondrial respiratory chain complex could be inhibited by copper. Copper could affect normal electron transport and mitochondrial oxidative phosphorylation, resulting in the inhibition of energy production. High concentrations of copper could disrupt intracellular ion balance and induce cytotoxicity. The oxidative stress could be induced by copper, leading to excessive ROS. Copper could reduce the mitochondrial membrane potential, lead to the leakage of apoptotic factors, and induce apoptosis. Copper could damage structure of gill, affect normal respiration of gill. This study provided fundamental data for exploring impacts of copper on gill function in aquatic organisms and potential mechanisms of copper toxicity.

Heavy metals (HMs) pollution in the aquatic environment: Role of probiotics and gut microbiota in HMs remediation

The presence of heavy metals (HMs) in aquatic ecosystems is a universal concern due to their tendency to accumulate in aquatic organisms. HMs accumulation has been found to cause toxic effects in aquatic organisms. The common HMs-induced toxicities are growth inhibition, reduced survival, oxidative stress, tissue damage, respiratory problems, and gut microbial dysbiosis. The application of dietary probiotics has been evolving as a potential approach to bind and remove HMs from the gut, which is called "Gut remediation". The toxic effects of HMs in fish, mice, and humans with the potential of probiotics in removing HMs have been discussed previously. However, the toxic effects of HMs and protective strategies of probiotics on the organisms of each trophic level have not been comprehensively reviewed yet. Thus, this review summarizes the toxic effects caused by HMs in the organisms (at each trophic level) of the aquatic food chain, with a special reference to gut microbiota. The potential of bacterial probiotics in toxicity alleviation and their protective strategies to prevent toxicities caused by HMs in them are also explained. The dietary probiotics are capable of removing HMs (50-90%) primarily from the gut of the organisms. Specifically, probiotics have been reported to reduce the absorption of HMs in the intestinal tract via the enhancement of intestinal HM sequestration, detoxification of HMs, changing the expression of metal transporter proteins, and maintaining the gut barrier function. The probiotic is recommended as a novel strategy to minimize aquaculture HMs toxicity and safe human health.

Gamma-aminobutyric acid enhances hypoxia tolerance of juvenile Chinese mitten crab (Eriocheir sinensis) by regulating respiratory metabolism and alleviating neural excitotoxicity

With climate change and intensive aquaculture development, environmental hypoxia in aquaculture water has become a common challenge for many aquatic species. Therefore, it is crucial to improve the hypoxic tolerance of animals through nutritional strategies. This study explored the positive role of dietary gamma-aminobutyric acid (GABA) supplementation in enhancing hypoxia tolerance of juvenile Eriocheir sinensis through respiratory regulation and alleviation of hypoxia-induced neural excitotoxicity. Acute hypoxia stress significantly up-regulated the mRNA expression level of hypoxia-inducible factor 1α, oxygen consumption rate and anaerobic respiratory metabolism-related enzyme activities. On the other hand, aerobic respiratory metabolism-related enzyme activities were significantly decreased. However, dietary GABA supplementation remodeled the respiratory metabolism pattern of juvenile crabs exposed to hypoxia stress. In addition, acute hypoxic stress significantly increased the contents of free glutamate and GABA in the nervous tissue. The expression levels of N-Methyl-d-aspartate-related receptor genes and calcium-dependent degradation enzyme-related genes were significantly up-regulated. Similarly, neuronal apoptosis rates, expression levels of apoptosis-related genes, and vesicular glutamate transporter genes were also significantly increased. The high-affinity neuronal glutamate transporter decreased significantly in the crabs exposed to hypoxia stress. However, dietary GABA supplementation could effectively prevent acute hypoxia stress-induced neural excitotoxicity. Furthermore, dietary GABA could significantly improve the redox status in vivo exposed to hypoxia stress. In conclusion, acute hypoxia stress can affect respiratory metabolism and redox state and induce neural excitotoxicity in juvenile E. sinensis. GABA supplementation could improve hypoxia tolerance through multiple physiological regulation pathways.

Effects of copper on non-specific immunity and antioxidant in the oriental river prawn (Macrobrachium nipponense)

The copper, as heavy metal has important impacts on the antioxidant and immune defense systems in aquatic organisms, and the toxic effects of copper can be accumulated and magnified with the food chain, thus posing a threat to food safety as well as ecosystems. This study explored the response of the antioxidant system and non-specific immunity in M. nipponense to copper stress. Low concentration of copper (0.05, 0.1 mg L^-1) had positive effects on the non-specific immunity in M. nipponense, while the non-specific immunity in M. nipponense could be affect negatively or even be inhibited by high copper concentration (0.15 mg L^-1). Even low concentrations of copper could cause oxidative stress, and high copper concentration (0.15 mg L^-1) could induce oxidative damage and even apoptosis, and thus causing damage to the antioxidant defense system in M. nipponense. Low concentration of copper could affect the gill and hepatopancreas structure in M. nipponense, but high level oxidative stress caused by high copper concentration could cause oxidative damage to these tissue, resulting in the destruction of gill and hepatopancreas. This study provides the safety concentration for using copper-containing fish drugs in the actual culture of M. nipponense and provides basic data for the toxicity mechanism of copper to M. nipponense.

Effect of Copper Nanoparticles and Ions on Epididymis and Spermatozoa Viability of Chinese Soft-Shelled Turtles Pelodiscus sinensis

Copper nanoparticles (CuNPs) have been widely used in various industrial and commercial applications, which become a potential threat to aquatic organisms. Nevertheless, their potential toxicity to the epididymis and sperm remains little known. In this study, we evaluated the effect of CuNPs and copper ions (CuSO4) on the spermatozoa viability, epididymal structure, antioxidant enzyme activity, and inflammatory cytokines in cauda epididymis of the Chinese soft-shelled turtle. Results showed that the spermatozoa viability of Chinese soft-shelled turtles decreased significantly with an increase in CuNPs or Cu ions concentrations. The epithelial cells of the epididymal duct of the Chinese soft-shelled turtles with the treatment of 5 mg kg−1 CuNPs were slightly swollen, and the connective tissue between the epididymal ducts was loose. The epithelial structure of the epididymal tube was severely damaged with an increase in Cu ion concentrations. Compared to the control, the antioxidative enzymes activities and the expression of IL-1β, TNF-α, and IL-6 mRNA in the epididymis significantly increased with the treatment of CuNPs or CuSO4. The present study revealed that Cu ions exert more harmful effect on the epididymis and spermatozoa viability of Chinese soft-shelled turtles than copper nanoparticles.

Accumulation and Depuration of Cd and its Effect on the Expressions of Metallothionein and Apoptotic Genes in Litopenaeus vannamei

We investigated cadmium (Cd) accumulation in muscles, gills and hepatopancreas of Litopenaeus vannamei following 48 h exposure to 5.25 mg/L, and depuration of Cd in these tissues on 1, 5 and 15 d post exposure. We also detected the expressions of metallothionein (MT), caspase-3 and p53 in hepatopancreas of shrimp exposed to 0, 5.25 and 10.5 mg/L Cd (the 24 h median lethal concentration, 24 h LC₅₀) at 0, 3, 12, 24 and 48 h. Cd accumulated with high concentration in hepatopancreas, and low concentration in muscles. Cd depurated fast in hepatopancreas and gills. MT expression increased in a time-dependent manner after Cd exposure. The p53 and caspase-3 increased at 12 and 24 h in 10.5 mg/L group. In conclusion, the accumulation and depuration of Cd in three tissues were tissues-specific. The changes of the expressions of MT, p53 and caspase-3, were stress response of L. vannamei under Cd exposure.

Cadmium-induced oxidative stress, metabolic dysfunction and metal bioaccumulation in adult palaemonid shrimp Palaemon macrodactylus (Rathbun, 1902)

The Palaemonid shrimp Palaemon macrodactylus is widely distributed in coastal areas and estuaries which are easily contaminated by various pollutants. However, the responses of this species to environmental toxicants are not well described. In the present study, adult individuals of P. macrodactylus were exposed to gradient concentrations of Cadmium (Cd) to evaluate its acute toxic effects, including bioaccumulation, induced oxidative stress and changed energy metabolism in this species. The medium lethal concentration (LC₅₀) of Cd at 24 h, 48 h, 72 h, and 96 h were 2.60, 0.88, 0.49 and 0.37 mg/L, respectively. Cd bioaccumulations in tissues of shrimp increased in a concentration-dependent manner, and higher concentration (50% 96 h-LC₅₀, 0.185 mg/L) of Cd exposure led to a maximum increase of Cd concentration by 14.8, 145.5 and 15.8 folds in gill, hepatopancreas and abdominal muscle. Cd exposure caused a significant inhibition on the activity of catalase (CAT), and total superoxide dismutase (T-SOD), decrease in the total antioxidant capacity (T-AOC), and an increase of malonadehyde (MDA) content, which indicated a damage to the antioxidant system of shrimp. Meanwhile, Cd exposure also led to a significant up-regulation in the expression level of metallothionein gene (MT), and down-regulations at the mRNA level of heat shock protein 70 (HSP70) and CAT. Moreover, Cd exposure significantly inhibited the oxygen consumption rate (22%), and increased the ammonia excretion rate (43%), hence lead to a significant decrease of the O:N ratio (45%) in shrimp. The results indicated that Cd exposure could induce obvious oxidative stress, energy metabolic dysfunction and bioaccumulation of Cd in P. macrodactylus. The data obtained from the present study would provide useful information for further understanding on the toxicological mechanism of Cd to crustaceans in coastal areas and estuaries.

Acute and sub-chronic effects of copper on survival, respiratory metabolism, and metal accumulation in Cambaroides dauricus

Trace metal contamination in the aquatic ecosystem occurs worldwide: although copper is an essential trace metal, it is considered as a pollutant at certain levels in China. Freshwater crayfish Cambaroides dauricus is a commercially important wild species in northeastern China, in which is an important heavy industry area. The population of C. dauricus was decreasing sharply due to the environmental pollution and human intervention over the past 20 years. However, nothing is known regarding the responses of this species to trace metal toxicants. This study aimed to determine the acute and chronic toxicity of Cu and its toxicological effects on respiratory metabolism, as well as Cu accumulation in C. dauricus. The acute (96 h) median lethal concentration (LC50) value of 32.5 mg/L was detected in C. dauricus. Then, acute (96 h; 8.24, 16.48 mg/L) and sub-chronic (14 days; 2.06, 4.12 mg/L) exposure in Cu was investigated by estimating the oxygen consumption rate, ammonium excretion rate, and Cu accumulation. Both acute and sub-chronic Cu exposure induced an inhibition of the oxygen consumption rate and ammonium excretion rate, and thereby, an increased O:N ratio. The shift in O:N ratio indicated a metabolic substrate shift towards lipid and carbohydrate metabolism under Cu stress. Cu accumulation in the hepatopancreas and muscles throughout the study was found to be time-dependent and concentration-dependent. The maximum accumulation in the hepatopancreas and muscle were almost 31.6 folds of the control after 14 days' exposure to 4.12 mg/L concentration. Based on the present work, we suggest that crayfish be considered a potential bioindicator of environmental pollution in freshwater systems. The study provides basic information for further understanding of the toxicological responses of this species to trace metals.

Comparative accumulation and transcriptomic analysis of juvenile Marsupenaeus japonicus under cadmium or copper exposure

Waterborne metals may be hazardous to aquatic organisms and trigger stress responses. The present study aimed to assess the effect of exposure to 100 μg/L cadmium (Cd) or copper (Cu) for 48 h on juvenile Marsupenaeus japonicus, in terms of bioaccumulation and the whole body transcriptome. The results demonstrated that Cu accumulation in M. japonicas was much higher than that of Cd. Meanwhile, transcriptome analysis identified 1802 and 2670 differentially expressed genes (DEGs) after 48 h exposure to 100 μg/L Cd and Cu, respectively. Among them, 851 DEGs responded to both metals. Cd and Cu stress shared genes were related to the cytoskeleton, immunity, antioxidation, and detoxification. Metallothionein 1 (MT1) was specifically induced in the Cd-stress response, while glycometabolism, heat shock protein 90 (HSP90), metallothionein 2 (MT2), apoptosis, and iron transport-related genes were changed specifically in response to Cu stress. In addition, real-time PCR was used to verify the expression patterns of 28 randomly selected DEGs. The sequencing and real-time PCR results were consistent. Moreover, based on the number of significantly modulated genes and their expression levels, we deduced that Cu acts as a stronger stress inducer than Cd in M. japonicus. The identified Cd and Cu stress related genes and pathways will provide new insights into the common and different molecular mechanisms underlying Cd and Cu toxicity effects in M. japonicus.

Copper exposure alters the metabolism of the blue crab Callinectes sapidus submitted to osmotic shock

Copper (Cu) is an essential metal capable to alter many metabolic and physiological processes in animal species, depending on the environmental concentration and salinity. The present study evaluated the effects of Cu exposure on the metabolism of the blue crab Callinectes sapidus under different osmotic situations. Crabs were acclimated at two different salinities conditions (30 and 2). Subsequently, they were exposed to Cu during 96 h at each salinity and under hypo-osmotic shock. Results demonstrated that Cu exposure increased whole-body oxygen consumption. In addition, the activity of LDH decreased while citrate synthase increased in anterior gills from animals submitted to hypo-osmotic shock. This scenario indicates extra stress caused by sudden environmental osmotic changes, as commonly observed in estuarine environments, when combined with copper exposure. Therefore, the activity of LDH and citrate synthase enzymes might be sensitive indicators for aquatic toxicology studies approaching Cu contamination in estuarine environments.

Respiratory Metabolism and Antioxidant Response in Chinese Mitten Crab Eriocheir sinensis During Air Exposure and Subsequent Reimmersion

Chinese mitten crab, Eriocheir sinensis, often suffers from severe air exposure stress during transportation and culture; high mortality occurs due to desiccation. In this study, the effects of air exposure stress (0, 2, 4, 8, and 16 h) and reimmersion (2, 6, 12 h) on respiratory metabolism and antioxidant responses in Chinese mitten crabs were studied under laboratory conditions. The results showed that air exposure and reimmersion had a significant impact on the oxygen consumption rate (OCR), ammonia excretion rate (AER), oxygen to nitrogen ratio (O:N), superoxide dismutase (SOD), catalase (CAT), succinate dehydrogenase (SDH), and lactate dehydrogenase (LDH). Significant interaction between air exposure and reimmersion was observed for OCR, AER, O:N, SOD, CAT, SDH, and LDH in Chinese mitten crab. During the air exposure stage, SOD, CAT, and LDH activities in the gills and hepatopancreas first increased and then decreased as air exposure time increased. All of these parameters were significantly higher in the 4-h air exposure group than those in the control group. All the parameters were significantly lower in the 16-h air exposure group than those in the control group, except LDH in the hepatopancreas. However, SDH activity gradually decreased with increased air exposure time, and all the air exposure groups were markedly lower than those in the control group in the gills. During the reimmersion stage, OCR, AER, and O:N restored to normal levels after 12-h reimmersion, except in the 16-h air exposure group, where OCR and O:N were significantly higher than those in the control group and AER was significantly lower than that in the control group. The LDH activity in all groups restored to normal levels after 12-h reimmersion. The SDH, SOD, and CAT activities of the 2- and 4-h air-exposed groups returned to normal levels after 12-h reimmersion; however, these three parameters were still significantly higher in the 16-h air-exposed group than in the control group in the gills and hepatopancreas. Overall, Chinese mitten crabs reduce aerobic respiration and increase anaerobic respiration capacity during desiccation. Under air exposure stress, Chinese mitten crabs change their energy utilization mode to meet their energy demands and adjust their respiratory metabolism and antioxidant enzymes activities to adapt to adverse environments.

Co-exposure of graphene oxide with trace elements: Effects on acute ecotoxicity and routine metabolism in Palaemon pandaliformis (shrimp)

Graphene oxide (GO) has been evaluated for application in environmental remediation and pollution control strategies. However, the side effects caused by the interactions of GO with classical pollutants in aquatic environments are still largely unknown. In this work, the ecotoxicological effects of GO, cadmium, zinc and the interactions between GO and these trace elements (co-exposure) were evaluated through acute toxicity tests and routine metabolism (i.e., oxygen consumption and ammonia excretion) in Palaemon pandaliformis (shrimp). After 96 h of exposure, GO did not present acute ecotoxicity at concentrations up to 5.0 mg L^-1. However, the association of GO with Cd or Zn increased the toxicity of these trace elements as demonstrated by the decrease in LC₅₀ values. The 96 h LC₅₀ of Cd associated with GO was 1.7 times less than the 96 h LC₅₀ of Cd alone. Similarly, the 96 h LC₅₀ of Zn associated with GO was 1.8 times less than the 96 h LC₅₀ of Zn alone. Additionally, the co-exposure of GO with trace elements impaired the routine metabolism of P. pandaliformis. Finally, the GO potentiated the ecotoxicological effects of Cd and Zn in the shrimp model. Future research on this emerging nanomaterial should focus on its use and disposal in aquatic ecosystems.

Respiratory Metabolism Responses of Chinese Mitten Crab, Eriocheir sinensis and Chinese Grass Shrimp, Palaemonetes sinensis, Subjected to Environmental Hypoxia Stress

Environmental hypoxia represents a major physiological challenge for Eriocheir sinensis and Palaemonetes sinensis and is a severe problem in aquaculture. Therefore, understanding the metabolic response mechanisms of E. sinensis and P. sinensis, which are economically important species, to environmental hypoxia and reoxygenation is essential. However, little is known about the intrinsic mechanisms by which E. sinensis and P. sinensis cope with environmental hypoxia at the metabolic level. Hypoxia-reoxygenation represents an important physiological challenge for their culture. In this study, respiratory metabolism and respiratory metabolic enzymes of E. sinensis and P. sinensis were evaluated after different hypoxia and reoxygenation times. The results showed that environmental hypoxia had a dramatic influence on the respiratory metabolism and activities of related enzymes. The oxygen consumption rates (OCR) significantly increased as hypoxia time increased, while the ammonia excretion rate (AER) was significantly lower than that in the control group after 8 h hypoxia. The oxygen to nitrogen ratio (O:N) in the control group was <16, indicating that all the energy substrates were proteins. After environmental hypoxia, the O:N significantly increased, and the energy substrate shifted from protein to a protein-lipid mixture. The OCR, AER, and O:N did not restore to initial levels after 2 h or 12 h reoxygenation and was still the same as after 8 h hypoxia. As environmental hypoxia time increased, succinate dehydrogenase (SDH) gradually decreased and lactate dehydrogenase (LDH) gradually increased. Both SDH and LDH were gradually restored to normal levels after reoxygenation. Therefore, environmental hypoxia should be avoided as much as possible during aquaculture breeding of E. sinensis and P. sinensis. Further, since OCR will significantly increase after a short period of reoxygenation, secondary environmental hypoxia due to rapid consumption of oxygen should also be avoided in aquaculture.

Acute waterborne cadmium toxicity in the estuarine pulmonate mud snail, Amphibola crenata

Freshwater pulmonate snails are sensitive to trace metals, but to date, the sensitivity of estuarine pulmonate snails to these important environmental toxicants is undescribed. Using the estuarine mud snail Amphibola crenata, effects of a 48-h exposure to waterborne cadmium (Cd) were investigated. The 48-h median lethal concentration (LC₅₀) was 50.4 mg L^-1, a value higher than that previously reported for any gastropod mollusc. Cadmium levels in the tissues of mud snails were highest in the viscera (digestive gland and gonad), with the foot muscle and remaining tissue compartment (kidney, mantle, remaining digestive tissues and heart) displaying significantly lower concentrations. Over a Cd exposure concentration range of 0-32 mg L^-1, Amphibola exhibited reduced oxygen consumption and elevated ammonia excretion in response to increasing Cd, the latter effect likely reflecting a switch to protein metabolism. This finding was supported by a declining oxygen: nitrogen ratio (O:N) as exposure Cd concentration increased. Other energy imbalances were noted, with a decrease in tissue glycogen (an effect strongly correlated with Cd burden in the viscera and foot muscle) and an elevated haemolymph glucose observed. An increase in catalase activity in the visceral tissues was recorded, suggestive of an effect of Cd on oxidative stress. The magnitude of this effect was correlated with tissue Cd burden. The induction of antioxidant defence mechanisms likely prevented an increase in levels of lipid peroxidation, which were unchanged relative to Cd exposure concentration in all measured tissues.

Uranium toxicity to aquatic invertebrates: A laboratory assay

Uranium mining is an environmental concern because of runoff and the potential for toxic effects on the biota. To investigate uranium toxicity to freshwater invertebrates, we conducted a 96-h acute toxicity test to determine lethal concentrations (testing concentrations up to 262 mg L^-1) for three stream invertebrates: a shredder caddisfly, Schizopelex festiva Rambur (Trichoptera, Sericostomatidae); a detritivorous isopod, Proasellus sp. (Isopoda, Asellidae); and a scraper gastropod, Theodoxus fluviatilis (Gastropoda, Neritidae). Next, we ran a chronic-toxicity test with the most tolerant species (S. festiva) to assess if uranium concentrations found in some local streams (up to 25 μg L^-1) affect feeding, growth and respiration rates. Finally, we investigated whether S. festiva takes up uranium from the water and/or from ingested food. In the acute test, S. festiva survived in all uranium concentrations tested. LC₅₀-96-h for Proasellus sp and T. fluviatilis were 142 mg L^-1 and 24 mg L^-1, respectively. Specimens of S. festiva exposed to 25 μg L^-1 had 47% reduced growth compared with specimens under control conditions (21.5 ± 2.9 vs. 40.6 ± 4.9 μg of mass increase animal^-1·day^-1). Respiration rates (0.40 ± 0.03 μg O₂·h^-1·mg animal^-1) and consumption rates (0.54 ± 0.05 μg μg animal^-1·day^-1; means ± SE) did not differ between treatments. Under laboratory conditions S. festiva accumulated uranium from both the water and the ingested food. Our results indicate that uranium can be less toxic than other metals or metalloids produced by mining activities. However, even at the low concentrations observed in streams affected by abandoned mines, uranium can impair physiological processes, is bioaccumulated, and is potentially transferred through food webs.

Acute toxic effects of zinc and mercury on survival, standard metabolism, and metal accumulation in juvenile ridgetail white prawn, Exopalaemon carinicauda

Ridgetail white prawn (Exopalaemon carinicauda) is widely distributed in Chinese coastal zones, especially in the Yellow Sea and Bohai Sea. It is not only considered as an important economic species in China, but also taken as a potential indicator species for the environmental pollution in the estuaries. At present, the responses of this species to environmental toxicants, including trace metal are not well understood. In this study, the acute toxic effects of zinc (Zn) and mercury (Hg) on the survival, oxygen consumption, ammonia-N excretion, and metal accumulation were investigated in the juveniles of E. carinicauda. The median lethal concentrations (LC₅₀) of Zn were 76.4, 44.0, 30.2, and 17.2mg/L, respectively, after the juveniles were exposed in for 24, 48, 72, and 96h, and the LC₅₀ of H_g was 0.212, 0.096, 0.084, and 0.065mg/L under the same exposure duration. The juveniles decreased the oxygen consumption by 51.4%, and increased ammonia-N excretion by 129% when they were exposed in Zn at the concentration of 76.4mg/L compared with their controls without Zn exposure, therefore the O:N ratio decreased by 82.9% compared with the control. Hg exposure with the concentration of 0.212mg/L caused the inhibition of oxygen consumption by 48.1% and increasement of ammonia-N excretion by 161%, and the atomic ratio of consumed oxygen to excreted ammonia-nitrogen (O:N ratio) decreased by 80.6% in the juveniles in comparison with the control. A concentration-dependent accumulation of heavy metals was observed in the gills, hepatopancreas and muscles of the experimental animals, with a maximum accumulation of 16.3 folds for Zn and 72.8 fold for Hg in the gills of the juveniles after 24h exposure. The data obtained from the present study would provide useful information for help further understanding on the toxicological responses of this species to trace metals.

Acute and sub-chronic effects of sub-lethal cadmium exposure on energy metabolism in the freshwater shrimp, Paratya curvirostris

Cadmium (Cd) is a toxic trace element enriched in waters through activities such as mining and agriculture. The freshwater shrimp Paratya curvirostris inhabits near-coastal, lowland streams potentially impacted by Cd, but nothing is known regarding its sensitivity to this metal. An acute (96h) median lethal concentration (LC₅₀) of 405µgL^-1 was derived for P. curvirostris, placing it among the most tolerant of freshwater shrimp species. Acute (4 d; 0, 50 and 100µgL^-1) and sub-chronic (10 d; 0, 25 and 50µgL^-1) exposures then investigated effects of Cd on energy metabolism (respiration rate, excretion rate, O:N ratio). In contrast to effects in previously studied species, Cd induced an increased respiration rate, which when coupled with an unchanged excretion rate, resulted in an increased O:N ratio. These data were explained by an increased reliance on carbohydrate and/or lipid as a metabolic substrate stimulated by increased metabolic costs of toxicant exposure. Similar effects were seen across all time-points, although the lowest effective Cd concentration decreased with increased exposure time. Overall, results suggest that Cd is unlikely to be a significant environmental stressor to P. curvirostris, except in highly contaminated freshwaters, and/or where Cd co-occurs with hypoxia.

Effects of Acute and Chronic Heavy Metal (Cu, Cd, and Zn) Exposure on Sea Cucumbers (Apostichopus japonicus)

Acute and chronic toxicity tests were conducted with sea cucumber (Apostichopus japonicus) exposed to heavy metals. Acute toxicity values (96 h LC50) were 2.697, 0.133, and 1.574 mg L⁻¹ for Zn, Cu, and Cd, respectively, and were ranked in order of toxicity: Cu > Cd > Zn. Under chronic metal exposure the specific growth rates of sea cucumbers decreased with the increase of metal concentration for all the three metals. After acute metal exposure, the oxygen consumption rate (OCR) decreased. The OCRs in all groups were significantly different than control (P < 0.05) except in the group treated with 1.00 mg L⁻¹ Zn (P < 0.05), where the increase of OCR was observed. The OCRs in groups chronically exposed to metals were significantly lower than that in the control group (P < 0.05). The activity of both pyruvate kinase (PK) and hexokinase (HK) in sea cucumbers followed: respiratory tree > muscle > intestine in natural sea water. After chronic Zn, Cu, and Cd exposure, the change pattern of HK and PK in respiratory tree, muscle, and intestine varied slightly. However, the activity of the enzyme showed a general trend of increase and then decrease and the higher the exposure concentration was, the earlier the highest point of enzyme activity was obtained.

Effects of Single and Joint Subacute Exposure of Copper and Cadmium on Heat Shock Proteins in Common Carp (Cyprinus carpio)

Copper (Cu) and cadmium (Cd) are the most common heavy metals that are easily detected in aquatic environments on a global scale. In this paper, we investigated the messenger RNA (mRNA) and protein levels of HSPs (HSP60, HSP70, and HSP90) in the liver of the common carp exposed to Cu, Cd, and a combination of both metals by real-time quantitative PCR and Western blot. The results indicated that in each exposure group, the mRNA levels of HSP60, HSP70, and HSP90 were increased significantly compared to the corresponding controls after 96 h of exposure (P < 0.05). A significant increase was observed in the HSP70 protein level in the high-dose Cu group and all of the Cd groups. Significant increases were also observed in the protein levels of HSP60 and HSP90 in the high combination group and the low combination group, respectively. These results indicated that the dynamics of HSP expression observed in the common carp support the role of HSPs as biochemical markers in response to environmental pollution and provided valuable insights into the adaptive mechanisms used by the common carp to adapt to the challenges of stressful environments.

Species sensitivity analysis of heavy metals to freshwater organisms

Acute toxicity data of six heavy metals [Cu, Hg, Cd, Cr(VI), Pb, Zn] to aquatic organisms were collected and screened. Species sensitivity distributions (SSD) curves of vertebrate and invertebrate were constructed by log-logistic model separately. The comprehensive comparisons of the sensitivities of different trophic species to six typical heavy metals were performed. The results indicated invertebrate taxa to each heavy metal exhibited higher sensitivity than vertebrates. However, with respect to the same taxa species, Cu had the most adverse effect on vertebrate, followed by Hg, Cd, Zn and Cr. When datasets from all species were included, Cu and Hg were still more toxic than the others. In particular, the toxicities of Pb to vertebrate and fish were complicated as the SSD curves of Pb intersected with those of other heavy metals, while the SSD curves of Pb constructed by total species no longer crossed with others. The hazardous concentrations for 5 % of the species (HC5) affected were derived to determine the concentration protecting 95 % of species. The HC5 values of the six heavy metals were in the descending order: Zn > Pb > Cr > Cd > Hg > Cu, indicating toxicities in opposite order. Moreover, potential affected fractions were calculated to assess the ecological risks of different heavy metals at certain concentrations of the selected heavy metals. Evaluations of sensitivities of the species at various trophic levels and toxicity analysis of heavy metals are necessary prior to derivation of water quality criteria and the further environmental protection.