The effects of long-term cadmium exposure on the growth and survival of juvenile bull trout (Salvelinus confluentus)

Impacts of heavy metals on early development, growth and reproduction of fish - A review

Heavy metals pollution causes a threat to the aquatic environment and to its inhabitants when their concentrations exceed safe limits. Heavy metals cause toxicity in fish due to their non-biodegradable properties and their long persistence in the environment. This review investigated the effects of heavy metals on early development, growth and reproduction of fish. Fish embryos/larvae and each developmental stage of embryo respond differently to the intoxication and vary from species to species, types of metals and their mode of actions, concentration of heavy metals and their exposure time. Many of the heavy metals are considered as essential nutrient elements that positively improve the growth and feed utilization of fishes but upon crossing the maximum tolerable limit these metals cause not only a hazard to fish health but also to human consumers and the disruption of ecological systems. Reduced gonadosomatic index (GSI), fecundity, hatching rate, fertilization success, abnormal shape of reproductive organs, and finally failure of reproduction in fish have been attributed to heavy metal toxicity. In summary, this review sheds light on the manipulation of fish physiology by heavy metals and seeks to raise sensitivity to the prevention and control of aquatic environmental contamination, particularly from heavy metals.

Metals and metalloids in freshwater fish from the floodplain of Tablas de Daimiel National Park, Spain

The Tablas de Daimiel National Park (TDNP) is a floodplain ecosystem in central Spain with a potential risk of heavy metal and metalloid pollution. The objective of this study was to know the accumulation of arsenic (As), cadmium (Cd), mercury (Hg), lead (Pb), and selenium (Se) in muscle of six species of freshwater fish from the floodplain of TDNP. We obtained muscle samples of Cyprinus carpio (n = 89); Squalius pyrenaicus (n = 16); Ameiurus melas (n = 9); Lepomis gibbosus (n = 8); Micropterus salmoides (n = 6) and Carassius auratus (n = 5). A. melas, which is a predatory species, had significantly higher Hg concentrations than omnivorous or herbivorous species (i.e. C. carpio). On the contrary, A. melas showed lower concentrations of As, Pb and Se than omnivorous species (i.e. S. pyrenaicus and L. gibbosus ). The concentration of Hg was positively associated with fish size in C. carpio and A. melas. Some individuals of C. carpio (5.7%) and S. pyrenaicus (12.5%) showed Pb muscle concentrations above the maximum residue levels established by the European legislation for human consumers. The observed muscle Se concentrations can be associated with adverse effects on fish such as blood changes, reduced growth, mortality of juveniles and reproductive failure. The accumulation of Se in this floodplain located in a seleniferous area and the contamination produced by spent Pb shot pellets used for hunting in the past are discussed as potential sources of the elevated levels of these two elements in fish from this floodplain wetland.

Effect on intestinal microbiota, bioaccumulation, and oxidative stress of Carassius auratus gibelio under waterborne cadmium exposure

Cadmium (Cd) is a hazardous pollutant known to exert various toxic effects and other sublethal effects on aquatic organisms, and induce a variety of adverse effects on human health, and can be commonly found in environment. The aim of this study was to explore the effects of waterborne Cd exposure on the intestinal microbiota, and Cd accumulation and oxidative response in Carassius auratus gibelio (C. gibelio). The fish were exposed to waterborne Cd at 0, 1, 2, and 4 mg/L for 30 days. Waterborne Cd exposure resulted marked alterations in the composition of microbiota. At the genus level, Bacteroides, Aeromonas, Akkermansia, Acinetobacter, Chryseobacterium, Shinella, Cetobacterium and Bacillus were significantly changed in Cd groups. The results obtained indicate that Cd exposure significantly increased the bioaccumulation level of Cd and profoundly affected antioxidant enzyme including superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), total antioxidant (T-AOC), malonaldehyde (MDA), and glutathione-S-transferase (GST). The present findings may provide a new framework for the role of gut microbiota in the response to environmental chemical contamination and in the pathogenesis of body disorders.

Egg case concentrate of Mantis religiosa abrogates the accumulation of cadmium in muscular and bone tissues of African catfish via activation of nitric oxide and myeloperoxidase activity

The study examined the prophylactic effect of praying mantis egg case powder (PMECP) against the accumulation of cadmium (Cd) in key tissues of African catfish (Clarias gariepinus). Thirty African catfish were randomly distributed into six (n = 5) groups. Group I was treated with normal fish diet (NFD) only. Group II was exposed to Cd + NFD. Group III was exposed to Cd + NFD + EC₅₀ PMECP. Group IV was exposed to Cd + NFD + EC₅₀ PMECP + 10% EC₅₀ PMECP. Group V was exposed to Cd + NFD + EC₅₀ PMECP + 20% EC₅₀ PMECP. Group VI was treated with EC₅₀ PMECP + NFD for 14 days. Inhibitory concentration (IC₅₀ ) of PMECP significantly scavenged free radicals in vitro with corresponding increase in the activity of myeloperoxidase (MPO) and nitric oxide (NO) level. PMECP also showed highest growth-rate pattern and downregulation of cavitation within the lamellae. Hence, PMECP may be a prophylactic agent against the Cd accumulation in African catfish. PRACTICAL APPLICATIONS: Mantis religiosa egg case is widely used in Asian traditional medicine and some part of West Africa, as prevention against several diseases such as urinary disorders, infertility, impotence, and shingles. Our previous investigation showed that Mantis religiosa egg case flour could prevent hepatotoxicity, inhibit respiratory dysfunction, and interrupt oxidative damage in lungs. It is also commonly utilized for its high protein content and clear airways potential. The results of this study revealed empirical evidence concerning the possible usage of PMECP as natural, alternative, and/or complementary protein supplement with prophylactic potentials. Hence, this study underlines PMECP as prophylactic agent in abrogating the accumulation of cadmium as well as improving the protein content in African catfish.

Cadmium exposure reduces the density of a specific ionocyte subtype in developing zebrafish

The present study examined the effects of waterborne cadmium (Cd) exposure on ionic balance and ionocyte density in developing zebrafish (Danio rerio) (0-4 days post-fertilization). Fish exposed to 1 or 10 μg Cd/L exhibited an increase in whole body Cd level. Exposure to 10 μg Cd/L also significantly reduced whole body content of Ca²⁺, but not other major ions (e.g., Na⁺, K⁺ and Mg²⁺). Such reduction was accompanied by a decrease in the density of Ca²⁺-transporting ionocytes, the Na⁺/K⁺-ATPase-rich cells (NaRCs). However, the densities of other ionocyte subtypes (e.g., Na⁺-transporting ionocytes) remained unchanged after exposure to 10 μg Cd/L. The potential interactive effects between water chemistry and Cd exposure on ionocyte density were examined further in Cd-exposed larvae acclimated to different water NaCl or Ca²⁺ levels. The results demonstrated that NaRC density increased in fish acclimated to low Ca²⁺ water, presumably increasing Ca²⁺ uptake for maintaining Ca²⁺ homeostasis. However, Cd exposure completely abolished the increased NaRC density in low water Ca²⁺ environments. The increased NaRCs over development was also reduced in Cd-exposed larvae. In conclusion, our study suggested that Cd exposure reduces the density of NaRCs and suppresses the compensatory regulation of NaRCs during acclimation to low water Ca²⁺ level. These inhibitory effects by Cd exposure ultimately disrupt Ca²⁺ balance in the early life stages of zebrafish.

Transcriptome analysis of genes expressed in the earthworm Eisenia fetida in response to cadmium exposure

Eisenia fetida earthworm is an ecotoxicologically important test species to monitor various pollutants. However, there is a little knowledge about the effects of cadmium (Cd) on earthworms at the transcriptional level. Firstly, we exposed E. fetida to soils supplemented with different concentrations (10, 30, 60 mg/kg soil) of Cd. Moreover, we depicted the characterization of gene expressions with E. fetida using high-throughput profiling of gene expression. In addition, a comparison of the gene expression profiles between each Cd treatment group and the control group suggested that differential expressional genes (DEGs) mainly enriched in enzyme activity, metabolism, oxidative stress, regeneration and apoptosis pathways. 8 DEGs from these pathways had been selected randomly to confirm the data of RNA-seq. Among these DEGs, six genes (metallothionein-2, phytochelatin synthase 1a, CuZn superoxide dismutase, sex determining region Y-box 2, sex determining region Y-box 4b, TP53-regulated inhibitor of apoptosis 1-like) up-regulated and 2 genes (beta-1,4-endoglucanase, apoptosis-stimulating of p53 protein 2-like) down-regulated in response to Cd exposure. The alteration of them indicated that earthworms could reduce the toxicity and bioavailability of Cd in polluted soil ecosystems through different pathways. This work lays an important foundation for linking earthworm transcriptional level with the ecological risk of Cd in soil ecosystem.

Negative effects of acute cadmium on stress defense, immunity, and metal homeostasis in liver of zebrafish: The protective role of environmental zinc dpre-exposure

In the study, zebrafish were exposed to 0 and 200 μg/L Zn for 8 weeks, and then both groups were transferred to water including 0, 100, and 200 μg/L Cd for 4 days, respectively. Acute Cd exposure caused negative effects on stress defense, immune, and metal transport systems by increasing lipid peroxidation, iNOS activity and mRNA levels of il-6 and inos, and decreasing Cu/Zn-SOD and HSP70 levels, and mRNA levels of sod1, cat, hsp70, p65, mtf-1, znt5, zip7, atp7a, and atp7b. Lipid peroxidation was significantly reduced by Zn pre-exposure under Cd exposure, which may be explained by the enhanced stress defense capacity and the weaken inflammatory response. Firstly, Zn pre-exposure increased MTs and HSP70 levels and CAT activity in Cd-free water, which may facilitate fish quick response to Cd. Secondly, Zn pre-exposure reduced Cd accumulation at 100 and 200 μg/L Cd, down-regulated il-6 and il-1β at 100 μg/L Cd and p65 at 200 μg/L Cd, and increased Cu/Zn-SOD and CAT activities at 200 μg/L Cd. Thirdly, Zn pre-exposure alone up-regulated transcription factors (hsf1, hsf2, and mtf-1, and nrf2) and their target genes (sod1, cat, hsp70, and mt2) under Cd exposure in a dose-dependent manner. It should be noted that Zn pre-exposure down-regulated several metal transport genes dramatically at 0 and 100 μg/L Cd, which may be an important mechanism for reducing Cd import into livers. Overall, long-term and environmental Zn pre-exposure mitigated Cd toxicity by the enhanced stress defense capacity and the down-regulated metal transport and inflammatory responses.

Potentially toxic elements in muscle tissue of different fish species from the Sava River and risk assessment for consumers

Fish from the Sava River are consumed daily by the local people: therefore, concern has been raised about the health implications of eating contaminated fish. In the present study, potentially toxic elements (PTE), such as Zn, Cu, Cr, Ni, Cd, Pb, As, Hg, and methylmercury (MeHg), were determined in ichthyofauna that are commonly consumed. PTE were determined in the fish muscle tissue. Fish were sampled at 12 locations from the source of the Sava River to its confluence with the Danube River during two sampling campaigns, namely; in 2014 under high water conditions and in 2015 under normal water conditions. Due to the different water regimes, different fish species were collected for chemical analysis. We observed that the concentrations of elements analysed in the fish muscle tissue were generally very low, except for those of Hg. Moreover, more than 90% of Hg present in the fish was in its most toxic form, namely MeHg. Especially in fish from the 2015 sampling campaign, Hg and MeHg concentrations increased with fish size, trophic level, and in the downstream direction. In addition, for Pb and As, and to some extent for Cd and Cr, spatial differences were detected in both years. The highest concentrations of PTE were detected in fish from sites with intensive industrial and agricultural activities. The consumption of fish in general does not pose a health risk for the PTE studied, except for Hg/MeHg at selected contaminated sites.

Inconsistent responses of liver mitochondria metabolism and standard metabolism in Silurus meridionalis when exposed to waterborne cadmium

We investigated the standard metabolic rate and liver mitochondria metabolism of the southern catfish when exposed to waterborne cadmium. Juvenile southern catfish were exposed to waterborne cadmium concentrations (0, 62.5, 125, 250 and 500 μg/L, respectively) for 8 weeks, and the final body mass, the standard metabolic rate, the state III respiration rate, the activity of cytochrome C oxidase (CCO) of liver mitochondria, and the hepatosomatic index (HSI) were determined. The results showed that the 62.5 μg/L, 125 μg/L, and 250 μg/L experiment groups had a significantly higher standard metabolic rate than that of the control group. Standard metabolic rate in the 500 μg/L experiment group did not differ from the control group. State III respiration rate of liver mitochondria decreased with an increase in cadmium concentration. The 125 μg/L, 250 μg/L, and 500 μg/L experiment groups had a significantly lower state III respiration rate than that of the control group. The activity of CCO in the 500 μg/L experiment group was significantly lower than that of the control group. These results suggest that at low cadmium concentrations, the southern catfish could continuously improve the standard metabolism to provide extra energy in response to the cadmium stress. Cadmium exposures caused damage to the structure and function of liver mitochondria and decreased the activity of mitochondria enzymes, which results in a decrease in the energy of the liver metabolism. The adjustment of the metabolism of liver mitochondria in southern catfish was inconsistent with the adjustment of individual standard metabolism.

Therapeutic Effect of Intestinal Autochthonous Lactobacillus reuteri P16 Against Waterborne Lead Toxicity in Cyprinus carpio

Harmful effects of heavy metals are myriad. Lead (Pb) from soil and atmosphere contaminates water bodies and affects the aquatic animals. Our previous study confirmed the in vitro probiotic potential of Lactobacillus reuteri against Pb toxicity, but further investigation is necessary for gaining insights into the related protection mode. Therefore, in this study, we investigated the protective effects of the potential probiotic L. reuteri P16 against waterborne Pb exposure-induced toxicity in the freshwater fish Cyprinus carpio. Fish (average weight: 23.16 ± 0.73 g) were allocated to four groups (control, Pb only, Pb + L. reuteri P16, and L. reuteri P16 only) and Pb groups were exposed to waterborne Pb (1 mg L⁻¹) for 6 weeks. L. reuteri P16 (10⁸ CFU g⁻¹) supplemented diet was provided twice daily. Growth performances, hemato-biochemical parameters, innate immune responses, intestinal microbiota, and Pb accumulation in tissues were measured at the end of the trial. When the fish were exposed to Pb, dietary supplementation of L. reuteri P16 effectively decreased mortality and accumulation of Pb in tissues, and improved the growth performance. Co-treatment with Pb and L. reuteri P16 alleviated Pb exposure-induced oxidative stress, reversed alterations in hemato-biochemical parameters, improved innate immune parameters, and restored intestinal enzymatic activities. Moreover, L. reuteri P16 supplementation reversed the changes in intestinal microbiota in Pb-exposed fish. Furthermore, Pb exposure decreased the expressions of pro-inflammatory cytokines (TNF-α, IL-1β). However, the expression of heat shock proteins (HSP70 and HSP90) increased, which might have increased the cellular stress. Interestingly, the Pb-induced alterations of gene expressions were reversed by L. reuteri P16 supplementation. Thus, dietary administration of the potential probiotic L. reuteri P16 had several beneficial effects on growth performance and immune responses, decreased Pb accumulation in tissues, and reversed alterations in hematological responses of C. carpio. Furthermore, it offered direct protection against Pb-induced oxidative stress. Therefore, L. reuteri P16 may be a novel dietary supplement for enhancing growth performance and preventing Pb-exposure-induced toxicity in fish in aquaculture and aquatic products.

The role of some feed additives in fish fed on diets contaminated with cadmium

The decline of cadmium pollution in fish farms is needed by any adequate method. The present study was designed to explore the effect of dietary cadmium contamination and its amelioration by using dietary clay, probiotic (Bactocell®), vitamin C, and vitamin E supplementation in Nile tilapia fish diet on growth rate, feed efficiency, blood components, and cadmium residues. Fish were separated into 15 groups, each group of fish was stocked into three aquaria and each contains 20 fishes. The fish of the first five groups were fed the basal diet, the second five groups were fed the basal diet contaminated with 25 mg cadmium/kg, and the third five groups were fed the same diet contaminated with 50 mg cadmium/kg. Within each dietary cadmium level, the first group was fed the diet without any supplementation, the second was fed the diet supplemented with natural clay (bentonite) at level 3%, the third group was fed the diet supplemented with 1 g Bactocell®/kg, the fourth group was fed the diet supplemented 50 mg vitamin E/kg, and the fifth group was fed the diet supplemented with 100 mg vitamin C/kg. Live body weight, daily body weight gain, and feed intake of Nile tilapia decreased significantly (P < 0.001) with increasing dietary cadmium level, while feed conversion was impaired. Fish group fed on diets contaminated with 50 mg cadmium/kg recorded the lowest live body weight and weight gain. Serum total protein and albumin concentration significantly (P < 0.001) decreased, while serum creatinine, AST, and ALT significantly (P < 0.001) increased with increasing cadmium level in fish diets. Blood hemoglobin and total erythrocyte (RBCs) significantly (P < 0.001 or 0.05) decreased with cadmium contamination in fish diets, while leukocytes were insignificantly affected. Body cadmium residues increased significantly (P < 0.001) by increasing cadmium level in fish diets. Live body weight, daily body weight gain, and feed intake of Nile tilapia increased significantly (P < 0.001) with feed additive supplementation in diets, also while feed conversion improved. Fish group fed on diets supplemented with probiotic Bactocell® or natural clay recorded higher body weight and gain rate than the other experimental groups. Serum total protein, blood hemoglobin, and total erythrocyte increased, while urea-N, creatinine, ALT, AST, and leukocytes decreased as affected with the feed additive supplementation. Feed additive supplementation in fish diets significantly (P < 0.001) decreased cadmium residues in fish bodies. Irrespective of dietary cadmium level, feed additive supplementation in fish diet improved the growth rate and decreased the concentrations of serum creatinine and ALT. The obtained results indicated that feed additive supplementation could modify the function of the kidney and liver in fish exposed to the cadmium toxicity.

Effects of chronic waterborne cadmium and zinc interactions on tissue-specific metal accumulation and reproduction in fathead minnow (Pimephales promelas)

The present study was designed to evaluate the interactive effects of chronic waterborne cadmium (Cd) and zinc (Zn) on tissue-specific metal accumulation and reproduction in fathead minnow (Pimephales promelas). Trios (1 male: 2 female; n=6-7) of fish were exposed for 21 days to: (i) control (no added Cd or Zn), (ii) waterborne Cd (7µg/L), (iii) waterborne Zn (170µg/L), and (iv) Cd and Zn in mixture (7 and 170µg/L, respectively). Exposure to Cd or Zn alone did not elicit any significant effect on reproductive output (cumulative egg production) relative to the control, however exposure to Cd and Zn in mixture resulted in a ~50% decrease in fish fecundity. Plasma estradiol in females was reduced by Cd and Zn exposures, both individually and in mixture, with the maximum reduction in the metal mixture exposure. The expression of hepatic estrogen receptor genes (ER-α and ER-β) in females was affected by exposure to Zn, alone and in mixture with Cd, but not to Cd alone, whereas hepatic vitellogenin gene expression was downregulated across all treatments. Increased follicular atresia in the ovary was also recorded, but only in fish exposed to Cd and Zn in mixture. The interactions of Cd and Zn in mixture decreased Cd accumulation in tissues (gill and liver), however no reciprocal reduction in tissue Zn accumulation was observed. In addition, the expression of the hepatic metallothionein gene was upregulated following exposure to Zn, alone and in combination with Cd, with no additive effects in the latter treatment. Overall, our findings suggest that chronic exposure to waterborne Cd and Zn in mixture may induce additive reproductive toxicity, essentially by disrupting estrogen-mediated functions in fish.

Toxic effects on bioaccumulation and hematological parameters of juvenile rockfish Sebastes schlegelii exposed to dietary lead (Pb) and ascorbic acid

Juvenile rockfish, Sebastes schlegelii (mean length 11.3 ± 1.2 cm, and mean weight 32.5 ± 4.1 g) were exposed for four weeks to dietary lead (Pb²⁺) at 0, 120, and 240 mg/L and ascorbic acid (AsA) at 100, 200, and 400 mg/L. The exposure concentrations and duration of significant Pb-induced accumulations in specific tissues of S. schlegelii were assessed. High levels of ascorbic acid significantly attenuated accumulations following exposure to dietary Pb. Dietary Pb exposure caused a significant increase in blood Pb concentrations, whereas red blood cell (RBC) count, hematocrit, and hemoglobin were significantly decreased. Notable changes were also observed in plasma calcium, magnesium, glucose, cholesterol, glutamic oxaloacetic transaminase (GOT), and glutamic pyruvate transaminase (GPT). The growth performance of S. schlegelii was significantly decreased. High doses AsA supplemention were effective in attenuating the changes brought about by dietary Pb exposure.

Interactive effects of chronic waterborne copper and cadmium exposure on tissue-specific metal accumulation and reproduction in fathead minnow (Pimephales promelas)

The present study was carried out to examine the interactive effects of chronic waterborne copper (Cu) and cadmium (Cd) on tissue-specific metal accumulation and reproduction in fathead minnow (Pimephales promelas). Trios (1 male: 2 female; n=5) of fish were exposed for 21days to: (i) control (no added Cu or Cd), (ii) waterborne Cu (75μg/L), (iii) waterborne Cd (5μg/L), and (iv) Cu and Cd mixture (75 and 5μg/L, respectively). Reproductive output (cumulative egg production) was significantly reduced by Cu but not by Cd. Interestingly however, no spawning occurred in fish exposed to the mixture of waterborne Cu and Cd. In general, both Cu and Cd accumulation in target tissues (gill, liver, gonad and carcass) increased significantly in fish exposed to Cu and Cd mixture, and no interaction between Cu and Cd accumulation was observed in any tissues, except in the liver where Cu accumulation was significantly reduced by Cd. The expression of female hepatic estrogen receptor genes (ER-α and ER-β) was most significantly elevated in fish exposed to Cu and Cd mixture, whereas vitellogenin gene expression was reduced maximally in the same exposure. Similarly, the hepatic expression of the metallothionein gene was most significantly upregulated in fish exposed to Cu and Cd mixture. Moreover, the circulating estradiol level in females was significantly decreased only during the co-exposure of waterborne Cu and Cd. Overall, the present study indicates that the interaction of chronic waterborne Cu and Cd exposure may elicit greater than additive effect on reproductive output in fish.

Tissue concentrations as the dose metric to assess potential toxic effects of metals in field-collected fish: Copper and cadmium

The present study examined the available literature linking whole-body tissue concentrations with toxic effects in fish species for copper and cadmium. The variability in effect concentration for both copper and cadmium among species occurred within an order of magnitude for all responses, whereas the range for lethal toxicity based on water exposure spanned approximately 4 to 5 orders of magnitude. Fish tissue concentrations causing adverse effects were just above background concentrations, occurring between 1 μg/g and 10 μg/g for copper and 0.1 μg/g to 4 μg/g for cadmium. The results also show that salmonids are especially sensitive to cadmium, which appears to be a function of chemical potency. No studies were found that indicated adverse effects without increases in whole-body concentration of these metals. This narrow range for dose-response implies that a toxicological spillover point occurs when the detoxification capacity of various tissues within the animal are exceeded, and this likely occurs at a similar whole-body concentration for all naïvely exposed fish species. Elevated whole-body concentrations in fish from the field may be indicative of possible acclimation to metals that may or may not result in effects for target species. Acclimation concentrations may be useful in that they signal excessive metal concentrations in water, sediment, or prey species for a given site and indicate likely toxic effects for species unable to acclimate to excess metal exposure. Using tissue residues as the dose metric for these metals provides another line of evidence for assessing impaired ecosystems and greater confidence that hazard concentrations are protective for all fish species.

Impact of acute Cd²⁺ exposure on the antioxidant defence systems in the skin and red blood cells of common carp (Cyprinus carpio)

Cd(2+)-induced oxidative stress and its effects on the expression of stress biomarkers and on macromolecule damage in the skin and blood of common carp were studied. Both tissues play important roles in the defence mechanisms against external hazards, serving as an anatomical barrier and as connecting tissue between the organs. In the skin, the production of peroxynitrite anion and hydrogen peroxide was almost doubled after exposure to 10 mg/L Cd(2+). The accumulation of these oxidant molecules suggests an intensive production of superoxide anion and nitrogen monoxide and the development of oxidative and/or nitrosative stress. Although the metallothioneins and the components of the glutathione redox system were activated in the skin, the accumulation of reactive intermediates led to the enhanced damage of lipid molecules after 24 h of metal exposure. In the blood, the basal levels of metallothionein messenger RNAs (mRNAs) were 2-2.5-fold of that measured in the skin. This high level of metallothionein expression could be the reason that the blood was less affected by an acute Cd(2+) challenge and the metallothionein and glutathione systems were not activated.

Development and application of the adverse outcome pathway framework for understanding and predicting chronic toxicity: II. A focus on growth impairment in fish

Adverse outcome pathways (AOPs) organize knowledge on the progression of toxicity through levels of biological organization. By determining the linkages between toxicity events at different levels, AOPs lay the foundation for mechanism-based alternative testing approaches to hazard assessment. Here, we focus on growth impairment in fish to illustrate the initial stages in the process of AOP development for chronic toxicity outcomes. Growth is an apical endpoint commonly assessed in chronic toxicity tests for which a replacement is desirable. Based on several criteria, we identified reduction in food intake to be a suitable key event for initiation of middle-out AOP development. To start exploring the upstream and downstream links of this key event, we developed three AOP case studies, for pyrethroids, selective serotonin reuptake inhibitors (SSRIs) and cadmium. Our analysis showed that the effect of pyrethroids and SSRIs on food intake is strongly linked to growth impairment, while cadmium causes a reduction in growth due to increased metabolic demands rather than changes in food intake. Locomotion impairment by pyrethroids is strongly linked to their effects on food intake and growth, while for SSRIs their direct influence on appetite may play a more important role. We further discuss which alternative tests could be used to inform on the predictive key events identified in the case studies. In conclusion, our work demonstrates how the AOP concept can be used in practice to assess critically the knowledge available for specific chronic toxicity cases and to identify existing knowledge gaps and potential alternative tests.

Metals in horseshoe crab eggs from Delaware Bay, USA: temporal patterns from 1993 to 2012

The health of horseshoe crab (Limulus polyphemus) eggs is important not only to maintain horseshoe crab populations, but because they are a resource for higher trophic levels, such as fish and shorebirds. We examined the concentrations of arsenic, cadmium, chromium, lead, manganese, mercury, and selenium in the eggs of horseshoe crabs from Delaware Bay (between New Jersey and Delaware, USA) in 1993, 1994, 1995, 1999, 2000, and 2012 to determine if there were significant temporal changes and if levels appear to pose a health risk to the crabs themselves, or to predators that consume them. All metal levels declined in horseshoe crab eggs between 1994 and 2012, although the declines were much less consistent for lead and chromium than that for mercury and cadmium. Levels of contaminants found in these eggs are well below those known to cause adverse effects in the crabs themselves or to organisms that consume them, such as migrating shorebirds.

Biological monitoring and B chromosome frequency in Bagre (Rhamdia quelen) in southeast Brazil

The genus Rhamdia presents B chromosomes which appear to be present in most species of the genus and thus represent an important characteristic in the evolutionary process. Furthermore, variations in environmental conditions can induce the presence of B chromosomes generated by alterations in the cell cycle, due to the interference from pollutants. The present study aimed to evaluate the cytogenetic aspects of individuals of a population of Rhamdia quelen collected in three areas with differing standards of water quality in the River Uberabinha, a region of the County of Uberlandia, Minas Gerais, Brazil. The Piscine Micronucleus Test results indicate significant genotoxic and cytotoxic potential at the sampling Sites. The chromosome count yielded the modal number 2n=58 with variance between zero and seven B chromosomes. The highest frequency of B chromosomes and the presence of karyotypes with seven supernumerary chromosomes occurred at Site 3, referring, thus, to the location of the highest genotoxic potential. There was a positive correlation between the presence of B chromosomes and the reduction in environmental quality. Therefore, the process of bioaccumulation of heavy metals in aquatic environments may be crucial to determine the presence of B chromosomes.

The effects of chronic exposure to environmentally relevant levels of waterborne cadmium on reproductive capacity and behaviour in fathead minnows

Cadmium (Cd) is a priority pollutant in aquatic ecosystems because of its highly toxic effects at low concentrations. Recent work has highlighted that at sublethal concentrations, Cd can impair the ability of fish to respond to important sensory cues. In the present study, we examined whether chronic exposure to environmentally relevant concentrations of waterborne Cd (1, 2.5 and 5 μg/L) can result in reproductive impairment in fathead minnows (Pimephales promelas) as measured by the standard Organization for Economic Cooperation and Development (OECD) 21-day reproductive assay. In addition, we also evaluated the effects of chronic waterborne Cd exposure on Cd accumulation in target tissues (liver and ovary) and plasma estradiol level in females and on the reproductive behaviour of fathead minnows. We found that the standard endpoints used in the OECD reproductive assays (e.g., egg production, number of spawning attempts, brood size) are more sensitive to Cd exposure than behavioural endpoints; however, the traditional method of interpreting reproductive impairment may underestimate toxic effects. Cadmium accumulation in liver and ovary of fish increased with increasing Cd exposure concentrations; however, plasma estradiol level remained unaffected. Reproductive capacity in fathead minnows decreased at waterborne Cd concentrations as low as 1 μg/L. The findings of our study have important implications for understanding the effects of chronic Cd exposure in metal-impacted feral fish populations.

Heavy metals in fish from the Aleutians: interspecific and locational differences

The objectives of this study were to examine levels of arsenic, cadmium, lead, mercury and selenium in edible tissue of seven species of marine fish collected from several Aleutian islands (in 2004) to determine: (1) interspecific differences, (2) locational differences (among Aleutian Islands), (3) size-related differences in any metal levels within a species, and (4) potential risk to the fish or to predators on the fish, including humans. We also compared metals levels to those of three other fish species previously examined in detail, as well as examining metals in the edible tissue of octopus (Octopus dofleini). Octopus did not have the highest levels of any metal. There were significant interspecific differences in all metal levels among the fish species, although the differences were less than an order of magnitude, except for arsenic (mean of 19,500 ppb in Flathead sole, Hippoglossoides elassodon). Significant intraisland variation occurred among the four sites on Amchitka, but there was not a consistent pattern. There were significant interisland differences for some metals and species. Mercury levels increased significantly with size for several species; lead increased significantly for only one fish species; and cadmium and selenium decreased significantly with size for halibut (Hippoglossus stenolepis). The Alaskan Department of Health and Social Services supports unrestricted consumption of most Alaskan fish species for all people, including pregnant women. Most mean metal concentrations were well below the levels known to adversely affect the fish themselves, or predators that consume them (including humans), except for mercury in three fish species (mean levels just below 0.3 ppm), and arsenic in two fish species. However, even at low mercury levels, people who consume fish almost daily will exceed guideline values from the Centers for Disease Control and the Environmental Protection Agency.

Copper, zinc, and cadmium body concentrations in Hexaplex trunculus collected from the Tunisian coast

Copper, Zn, and Cd were analyzed in the soft tissues of the edible gastropod Hexaplex trunculus collected from seven localities along the Tunisian coast. The body concentration of these metals was significantly different depending on the gender and site. Copper and Zn varied, respectively, from 47.70 to 343.64 μg/g dry weight (dw) and 149.46 to 530.44 μg/g dw, being higher in males. Cadmium varied from 0.22 to 18.95 μg/g dw and was always higher in females. Overall, the highest concentrations of the three metals were all recorded in Gabès fishing harbor. Comparison of metal concentrations with the European standards compiled by the Food and Agriculture Organization showed that values exceeded standards in several localities. Imposex had been previously recorded in H. trunculus along the Tunisian coast; however, it does not seem to be related with Cu, Zn, and Cd pollution because the body concentration of these metals is not correlated with imposex degree. Nevertheless, interactive effects resulting from the combination of different pollutants and other stressors cannot be disregarded.

Differential effect of waterborne cadmium exposure on lipid metabolism in liver and muscle of yellow catfish Pelteobagrus fulvidraco

The present study was conducted to investigate the effect of waterborne cadmium (Cd) exposure on lipid metabolism in liver and muscle of juvenile yellow catfish Pelteobagrus fulvidraco. Yellow catfish were exposed to 0 (control), 0.49 and 0.95 mg Cd/l, respectively, for 6 weeks, the lipid deposition, Cd accumulation, the activities and expression level of several enzymes as well as the mRNA expression of transcription factors involved in lipid metabolism in liver and muscle were determined. Waterborne Cd exposure reduced growth performance, but increased Cd accumulation in liver and muscle. In liver, lipid content, the activities and the mRNA expression of lipogenic enzymes (6-phosphogluconate dehydrogenase (6PGD), glucose-6-phosphate dehydrogenase (G6PD), fatty acid synthetase (FAS)) and lipoprotein lipase (LPL) activity increased with increasing waterborne Cd concentrations. However, the mRNA expressions of LPL and peroxisome proliferators-activated receptor (PPAR) α were down-regulated by Cd exposure. Carnitine palmitoyltransferase 1 (CPT1) activity as well as the mRNA expressions of CPT1 and PPARγ showed no significant differences among the treatments. In muscle, lipid contents showed no significant differences among the treatments. The mRNA expression of 6PGD, FAS, CPT1, LPL, PPARα and PPARγ were down-regulated by Cd exposure. Thus, our study indicated that Cd triggered hepatic lipid accumulation through the improvement of lipogenesis, and that lipid homeostasis in muscle was probably conducted by the down-regulation of both lipogenesis and lipolysis. Different variation patterns of lipid metabolism to waterborne Cd exposure indicated the tissue-specific regulatory effect of lipid metabolism under waterborne Cd exposure. To our knowledge, the present study provides, for the first time, evidence that waterborne chronic Cd exposure can disturb the normal processes of lipid metabolism at both the enzymatic and molecular levels, and in two tissues (the liver and muscle).

Influence of cadmium exposure on growth and fecundity of freshwater mosquitofish Gambusia affinis: in situ and in vivo studies

This study aims to investigate the effect of cadmium (Cd) exposure on growth and fecundity of mosquitofish Gambusia affinis. For this purpose, two natural populations of pregnant females of G. affinis captured from two sites were differently contaminated with Cd (S1 present Cd levels 5-fold higher than S2) and a sublethal exposure to 0.4 mg CdCl(2)/L (10% of LC(50)) during 56 days was conducted in vivo. The length-weight regression revealed a significant difference in the growth between these two populations. A significant difference in fecundity was also noted between the two populations. Indeed, the embryo numbers in pregnant females captured from S1 are significantly higher than those noted in pregnant females from S2 (21.17±5 and 7.97±2.12, respectively; p<0.05). Following Cd exposure, we noted a growth perturbation resulting in lower values of both indices BWG and SGR following 7 and 21 days (-5.21 and -1.18 for BWG, and -2.09 and -0.46 for SGR, respectively) and a recuperation of growing weight at 42 and 56 days (1.32 and 1.71 for BWG, and 0.45 and 0.54 for SGR, respectively). For CF index, we observed a significant difference (p<0.05) between control and Cd groups at 7 and 21 days of exposure, and at 21 and 56 days respectively for HSI and GSI indices. Furthermore, Cd contents in both tissues (liver and yolk sac) and fractions (cytosolic and membrane) are significantly different between groups during experimentation. In addition, the Cd contents noticed in the liver membrane fraction are significantly higher than those noted in the yolk sac tissue. The MTs levels revealed a significant difference between the control and Cd groups. In liver tissue, a significant difference was noted, in MTs levels, during the Cd exposure (7, 21, 42, and 56 days) while in the yolk sac tissue the difference was noted at 42 days of exposure. Taken together, these results imply the potential negative effect of Cd on physiological status of G. affinis as evidenced by decreasing growth and fecundity rate.

Tissue-specific accumulation of cadmium and its effects on antioxidative responses in Japanese flounder juveniles

This study investigated the accumulation of cadmium (0-8 mg Cd L⁻¹) and its toxicological effects on oxidative stress biomarkers in different tissues of Japanese flounder juveniles. Following Cd exposure for 28 d, accumulation of Cd in fish was dose-dependent and tissue-specific, with the greatest accumulation in the liver, followed by the kidney, gill, and muscle. Although the gill and liver mounted active antioxidant responses at ≥ 4 mg L⁻¹ Cd including a decrease in glutathione level and GST and GPx activities, the antioxidant response failed to prevent lipid peroxidation induction in these organs. In the kidney, increased GPx and GST activities and decreased SOD activity were observed in fish exposed to high Cd concentrations, but LPO levels did not significantly differ among the exposure concentrations. The gill was most sensitive to oxidative damage, followed by the liver; the kidney was the least affected tissue.

Antioxidant responses, hepatic intermediary metabolism, histology and ultrastructure in Synechogobius hasta exposed to waterborne cadmium

The present study was conducted to determine antioxidant responses, hepatic intermediary metabolism, histology and ultrastructure in Synechogobius hasta after a 15-days of waterborne cadmium (Cd) exposure at the concentrations of 0 (control), 0.10, 0.17 and 0.29 mg Cd/l (corresponding to 0, 12.6%, 21.5% and 36.7% of 96 h LC₅₀), respectively. Growth performance and survival declined, but hepatosomatic index (HSI) increased with increasing waterborne Cd levels (P < 0.05). Waterborne Cd exposure also significantly increased lipid contents in whole body and liver (P < 0.05), and Cd accumulation in whole body, muscle and vertebrae. Waterborne Cd exposure changed hepatic enzymatic activities involved in intermediary metabolism, induced antioxidant responses and increased lipid peroxidation level in the gill, liver and spleen. Waterborne Cd exposure also caused considerable histological alterations of gill, liver and spleen, led ultrastructures damage of liver and spleen of fish, and induced fatty liver for this fish species.

Utility of tissue residues for predicting effects of metals on aquatic organisms

As part of a SETAC Pellston Workshop, we evaluated the potential use of metal tissue residues for predicting effects in aquatic organisms. This evaluation included consideration of different conceptual models and then development of several case studies on how tissue residues might be applied for metals, assessing the strengths and weaknesses of these different approaches. We further developed a new conceptual model in which metal tissue concentrations from metal-accumulating organisms (principally invertebrates) that are relatively insensitive to metal toxicity could be used as predictors of effects in metal-sensitive taxa that typically do not accumulate metals to a significant degree. Overall, we conclude that the use of tissue residue assessment for metals other than organometals has not led to the development of a generalized approach as in the case of organic substances. Species-specific and site-specific approaches have been developed for one or more metals (e.g., Ni). The use of gill tissue residues within the biotic ligand model is another successful application. Aquatic organisms contain a diverse array of homeostatic mechanisms that are both metal- and species-specific. As a result, use of whole-body measurements (and often specific organs) for metals does not lead to a defensible position regarding risk to the organism. Rather, we suggest that in the short term, with sufficient validation, species- and site-specific approaches for metals can be developed. In the longer term it may be possible to use metal-accumulating species to predict toxicity to metal-sensitive species with appropriate field validation.

Impacts and pathways of mine contaminants to bull trout (Salvelinus confluentus) in an Idaho watershed

Metals contamination from mining activities is a persistent problem affecting aquatic ecosystems throughout mining districts in the western USA. The Gold Creek drainage in northern Idaho has a history of mining within its headwaters and contains elevated sediment concentrations of As, Cd, Cu, Pb, and Zn. To determine system-wide impacts of increased metals, we measured concentrations of metals in water, sediment, and benthic macroinvertebrate tissues and related them to whole-body fish tissues and histopathological alterations in native salmonids. Water concentrations were higher than those in reference areas, but were below water quality criteria for protection of aquatic biota for most of the study area. Sediment and benthic macroinvertebrate tissue concentrations for all metals were significantly higher at all sites compared with the reference site. Fish tissues were significantly higher for all metals below mine sites compared with the reference site, but only Cd and Pb were higher in fish tissues in the furthest downstream reach in the Gold Creek Delta. Metals concentrations in benthic macroinvertebrate tissues and fish tissues were strongly correlated, suggesting a transfer of metals through a dietary pathway. The concentrations within sediments and biota were similar to those reported in other studies in which adverse effects to salmonids occurred. We observed histopathological changes in livers of bull trout, including inflammation, necrosis, and pleomorphism. Our study is consistent with other work in which sediment-driven exposure can transfer up the food chain and may cause adverse impacts to higher organisms.

Accumulation and oxidative stress biomarkers in Japanese flounder larvae and juveniles under chronic cadmium exposure

This study investigated how Cd exposure affected oxidative biomarkers in Japanese flounder, Paralichthys olivaceus, at early life stages (ELS). Fish were exposed to waterborne Cd (0-48microg L(-1)) from embryonic to juvenile stages for 80days. Growth, Cd accumulation, activities of superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), glutathione S-transferase (GST, EC 2.5.1.18), and levels of glutathione (GSH) and lipid peroxidation (LPO) were investigated at three developmental stages. Flounder growth decreased and Cd accumulation increased with increasing Cd concentration. In metamorphosing larvae, CAT and SOD activities were inhibited and GSH level was elevated, while LPO was enhanced by increasing Cd concentrations. CAT and GST activities of settling larvae were inhibited but GSH level was elevated at high Cd concentrations. In juveniles, SOD activity and LPO level were increased but GST activity was inhibited as Cd concentration increased. Antioxidants in flounder at ELS were able to develop ductile responses to defend against oxidative stress, but LPO fatally occurred due to Cd exposure. These biochemical parameters could be used as effective oxidative biomarkers for evaluating Cd contamination and toxicity in marine environments: CAT, SOD, GSH, and LPO for metamorphosing stage; CAT, GSH, and GST for settling stage; and SOD, GST, and LPO for juvenile stage.

Comparative toxicity of cadmium in the commercial fish species Sparus aurata and Solea senegalensis

The induction of metallothionein-like proteins (MTLPs) as well as cadmium levels (Cd) was studied in tissues of gilthead sea bream Sparus aurata and flatfish Solea senegalensis after an intraperitoneal (i.p.) injection of cadmium (2.5 mg kg(-1) body weight). The liver, gills, intestine and blood of S. aurata as well as the liver and intestine of S. senegalensis were collected for analysis at 0, 3 and 6 days after the injection. Cd levels significantly increased in all tissues of the treated animals, and the highest accumulation was found in the liver in both species (p<0.05). Cadmium administration provoked significant inductions of MTLP synthesis in the liver and intestine of S. aurata (p<0.05), while no increase in these protein levels was recorded in tissues of S. senegalensis. Our findings imply that MTLP synthesis in S. aurata probably led to an enhanced ability to cope with the toxicant, whereas the MTLP induction in S. senegalensis was inhibited by the accumulated cadmium, as reflected by the mortality rate of this species. Under the experimental conditions, hepatic MTLPs appear to be a good indicator of the Cd level in S. aurata; however, no link was found between the cadmium concentration and MTLP induction in S. senegalensis, which suggests that MTLPs did not play a main role in detoxification by metal sequestration.

Environmental contaminants in freshwater fish and their risk to piscivorous wildlife based on a national monitoring program

Organochlorine chemical residues and elemental concentrations were measured in piscivorous and benthivorous fish at 111 sites from large U.S. river basins. Potential contaminant sources such as urban and agricultural runoff, industrial discharges, mine drainage, and irrigation varied among the sampling sites. Our objectives were to provide summary statistics for chemical contaminants and to determine if contaminant concentrations in the fish were a risk to wildlife that forage at these sites. Concentrations of dieldrin, total DDT, total PCBs, toxaphene, TCDD-EQ, cadmium, chromium, mercury, lead, selenium, and zinc exceeded toxicity thresholds to protect fish and piscivorous wildlife in samples from at least one site; most exceedences were for total PCBs, mercury, and zinc. Chemical concentrations in fish from the Mississippi River Basin exceeded the greatest number of toxicity thresholds. Screening level wildlife risk analysis models were developed for bald eagle and mink using no adverse effect levels (NOAELs), which were derived from adult dietary exposure or tissue concentration studies and based primarily on reproductive endpoints. No effect hazard concentrations (NEHC) were calculated by comparing the NOAEL to the food ingestion rate (dietary-based NOAEL) or biomagnification factor (tissue-based NOAEL) of each receptor. Piscivorous wildlife may be at risk from a contaminant if the measured concentration in fish exceeds the NEHC. Concentrations of most organochlorine residues and elemental contaminants represented no to low risk to bald eagle and mink at most sites. The risk associated with pentachloroanisole, aldrin, Dacthal, methoxychlor, mirex, and toxaphene was unknown because NOAELs for these contaminants were not available for bald eagle or mink. Risk differed among modeled species and sites. Our screening level analysis indicates that the greatest risk to piscivorous wildlife was from total DDT, total PCBs, TCDD-EQ, mercury, and selenium. Bald eagles were at greater risk to total DDT and total PCBs than mink, whereas risks of TCDD-EQ, mercury, and selenium were greater to mink than bald eagle.

The influence of water quality on the embryonic survivorship of the Oregon spotted frog (Rana pretiosa) in British Columbia, Canada

In Canada, the Oregon spotted frog (Rana pretiosa) is a critically endangered species with only three known populations and an estimated breeding population of less than 400 located in isolated sites in the extreme south-west corner of British Columbia. Floating Nitex cages were used to assess embryonic survivorship in two populations of Oregon spotted frogs from 2002-2005. One population, near Aldergrove, BC experienced declines in population size while the other population, at Maria Slough, increased during the period 1997-2001. During embryo development, we measured trace metals, nutrients and physical parameters in the water at each site. These were used to test the hypothesis that water quality parameters were correlated with embryonic survivorship. During the study period in the declining population at Aldergrove R. pretiosa bred at two distinct sub sites (A and B) located 500 m apart within the wetland. Mean embryonic survivorship varied from 9% to 36% at sub site A and from 78% to 88% at sub site B whereas in the population in Maria Slough, the mean embryonic survivorship varied from 77% to 84%. Sulphate was the only water chemistry variable that differed significantly between the two study sites and was the highest at Maria Slough. A weak significant positive correlation was found between chloride and embryonic survivorship and conductivity and embryonic survivorship. A multiple regression model found conductivity was the only significant variable. We concluded that natural water chemistry conditions of low chloride and consequently low conductivity may be contributing to low embryonic survivorship in the population of R. pretiosa at MD Aldergrove, BC.

Potential marker enzymes and metal-metal interactions in Helisoma duryi and Lymnaea natalensis exposed to cadmium

In this study, we investigate the effects of exposure to cadmium and copper on Lymnaea natalensis and Helisoma duryi. The snails were dosed with Cd2+ or Cu2+ for a period of 96h. Snails dosed with Cd accumulated the metal significantly (P<0.05) in tissues but not in shells. Mortality was observed at approximately 1mg Cd/l of culture water. In tissues and shells of snails dosed with Cd or Cu, synergistic and antagonistic metal-metal interactions involving Cd, Cu, Zn, and Pb were observed and these may affect metal toxicity. Glutamate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase were assayed in whole snail tissue sub-cellular fractions of Cd-dosed snails. Generally, enzyme activity significantly increased at lower concentrations of Cd but decreased at high concentrations of the metal. However, mitochondrial alanine aminotransferase activity progressively declined with increasing Cd concentration. The changes in some of the enzymes' activities suggest biomarker potential.

Effect of cadmium on gonadal development in freshwater turtle (Trachemys scripta, Chrysemys picta) embryos

Prior studies on painted turtle (Chrysemys picta) sub-populations near the Massachusetts Military Reservation (MMR), a Superfund site on Cape Cod, Massachusetts, USA, suggest several reproductive deficits which may be related to xenobiotics. Several heavy metals, including cadmium, have been detected in Cape Cod surface water and sediments. The present study was carried out to investigate the effect of an environmentally relevant dose of cadmium on gonadal development during the end of the germ cell migration phase and post-natal gonadal maturation in freshwater turtles. Comparison of cadmium concentration in eggs of C. picta from Cape Cod showed that eggs from the impacted site animals had significantly higher cadmium in yolk than eggs from the reference site animals (7.23 +/- 1.95 ng/g vs. 1.31 +/- 0.50 ng/g). Gonadal structure and the number of proliferating germ cells of neonates derived from eggs of adult females from these sites showed no marked difference between sites. However, apoptosis of oocytes was significantly increased in neonate C. picta from the impacted pond compared to the reference pond. The effect of an administered environmentally relevant dose of cadmium on germ cell number and oocyte apoptosis was subsequently assessed in lab-reared Trachemys scripta, a closely related freshwater turtle species. Assessment of isotopic cadmium transmission showed that 6.29% of cadmium applied to the eggshell was transmitted through the eggshell to the yolk. The results showed that the total number of germ cells in cadmium-treated (1 microg/g) embryos was less than half that found in control embryos. The reduced germ cell number in Cd-treated embryos suggests that cadmium may reduce proliferation and/or delay migration of germ cells to the genital ridge. The effects of cadmium on turtle gonadal development were found to extend into 3 months post hatch. Proliferation of oocytes was not influenced by exposure to cadmium in ovo. In contrast, apoptosis of oocytes was significantly increased in cadmium exposed T. scripta. Since a lesion at the gonial stages will lead eventually to the depletion of more mature germ cells, the results for neonate turtles suggest that an environmental impact due to a xenobiotic mixture may enhance the rate of apoptosis, thus resulting in the reduction in follicle number seen in adult turtles from the impacted site. Overall, the data provide evidence that environmentally relevant doses of cadmium may affect gonadal developmental processes of freshwater turtles during embryonic and post-natal stages that may result in disruption of reproductive processes later in life.

Distinctive accumulation patterns of Cd(II), Cu(II), and Cr(VI) in tissue of the South American teleost, pejerrey (Odontesthes bonariensis)

The time- and concentration-dependent accumulation patterns of three environmentally relevant metals, with different chemical and biological properties, were comparatively evaluated in tissue of South American fish, pejerrey (Odontesthes bonariensis). Six-month-old juvenile pejerrey were exposed to 1, 5, or 10 microgl(-1) of Cd(2+); 10, 50, or 100 microgl(-1) of Cu(2+); or 100, 500, or 1000 microgl(-1) of Cr(6+) during 16 days. Tested concentrations ranged from those that caused no significant accumulation to those that induced growth reduction or even mortality (Cd and Cu). Concentration-dependent accumulation of Cd and Cr presented similar patterns, characterized by a linear and exponential relationship in the gill and liver, respectively, with a greater slope at longer exposure times. Differently, essential Cu showed a linear relationship in both tissues, and no slope increase was observed in the gill. The gill time-dependent accumulation pattern of Cd exhibited relatively long times to half-saturation (t(1/2(1))=36.6 days) and high-saturation values (S((1))=205.4 nmolg(-1)). The opposite pattern was observed for Cu (t(1/2(100))=0.6 days; S((100))=24.4 nmolg(-1)), while Cr showed an intermediate position (t(1/2(1000))=2.8 days; S((1000))=50.2 nmolg(-1)). In the liver, times to half saturation for the three metals were as follows: Cd=4.7 days; Cu=2.5 days; Cr=1.6 days. Conversely, different saturation concentrations were observed among metals, Cu (S((100))=102) presenting the highest values, Cd (S((10))=4.4) the lowest, and Cr presenting an intermediate position (S((1000))=24.7). Bioconcentration of non-essential Cd was high in the gill (2000-fold) and low in the liver (50-fold). On the other hand, the essential element Cu was poorly retained by the gill (15-fold) and accumulated mainly in the liver (50-fold). Differently, Cr was quickly and evenly accumulated by both organs, but barely bioconcentrating (2.5- and 1.5-fold levels as compared to the original in the gill and liver, respectively). The ratio of gill/liver concentration in exposed fish clearly differed from that of non-exposed fish, and was characteristic for each metal (Cd>1; Cu<1; Cr<9), representing a potential tool to assess exposure. The accumulation patterns of studied metals in the tissue of pejerrey corresponded more with those reported for sensitive than for tolerant fish species. Distinctive tissue accumulation patterns in relation to growth reduction and non-acute lethality suggests different target tissues for sub-chronic effects, and would partially explain differences in the relative toxicity of these metals.

Assessment and management of risk to wildlife from cadmium

Cadmium, a nonessential heavy metal that comes from natural and anthropogenic sources, is a teratogen, carcinogen, and a possible mutagen. Assessment of potential risk from cadmium requires understanding environmental exposure, mainly from ingestion, although there is some local exposure through inhalation. Chronic exposure is more problematic than acute exposure for wildlife. There is evidence for bioaccumulation, particularly in freshwater organisms, but evidence for biomagnification up the food chain is inconsistent; in some bird studies, cadmium levels were higher in species that are higher on the food chain than those that are lower. Some freshwater and marine invertebrates are more adversely affected by cadmium exposure than are birds and mammals. There is very little experimental laboratory research on the effects of cadmium in amphibians, birds and reptiles, and almost no data from studies of wildlife in nature. Managing the risk from cadmium to wildlife involves assessment (including ecological risk assessment), biomonitoring, setting benchmarks of effects, regulations and enforcement, and source reduction.

Heavy metals in Pacific cod (Gadus macrocephalus) from the Aleutians: location, age, size, and risk

Considerable attention has been devoted to the risks from mercury (Hg) and polychlorinated biphenyls (PCB) to high-level predators (including humans) who consume freshwater fish. Although the U.S. Food and Drug Administration (FDA) issued advisories because of Hg for four marine fish species, there are few data on lead (Pb), cadmium (Cd), or other metals in Bering Sea fish generally, or on the risk these levels pose to the fish themselves or to consumers of marine fish. Levels of arsenic (As), Cd, chromium (Cr), Pb, Hg, and selenium (Se) levels were examined in muscle and liver of 142 Pacific Cod (Gadus macrocephalus) collected in 2004 at Nikolski, Adak, Amchitka, and Kiska Islands in the Aleutian Chain (Alaska) in the Bering Sea/North Pacific Ocean, a major source of commercial fishing. One key objective was whether there were location, age, gender, and size effects on tissue concentration that might pose a risk to the fish or their predators (including humans). All fish were measured and weighed, and a subset was aged by examining otolith layers. As was higher in liver than in muscle (geometric mean 2420 versus 1590 ng/g or ppb wet weight), as were Cd (GM 224 versus 1.92) and Se (GM 1380 versus 165). Conversely, Cr was higher in muscle (76.8 versus 45 ppb), as were Pb (23.7 vs 12 ppb) and surprisingly Hg (128 versus 82 ppb). Adak, until recently a large military base, had the highest levels of As, Hg, and Se, while Amchitka had the highest Pb levels, but Nikolski, which generally had the lowest levels, had relatively high Pb in liver. In general, interisland differences were significant for most metals in muscle, but only for Cr in liver. Weight and length were positively related to age, but age tended to explain more of the variance in metal levels. The multiple regression relationships differed by tissue in an unanticipated manner. Location contributed significantly to the models for muscle Cd, Pb, Hg, and Se, but not for liver levels. Conversely the length by weight interaction entered all of the liver models but none of the muscle models. Se and Hg were positively but weakly correlated in both liver (tau = +0.16) and muscle tissue (tau = 0.12). Hg was positively correlated with length, weight, and age in muscle, but not in liver. As showed a significant negative correlation with size variable in both tissues, and Cr was negatively correlated in muscle. Cd was positively correlated with Hg, Se, and As. Between liver and muscle there were significant positive correlations for Hg (tau = .24), As (tau = .407), and Cr (tau = 0.17), but not for Pb, Cd, or Se. In this study, the only metals that might pose a risk to cod-eating predators is Hg, as well as some of the higher values of Pb at Amchitka and Nikolski . The U.S. Environmental Protection Agency (EPA) reference dose (RfD) (not available for lead) was used to evaluate the risk to people consuming an 8-ounce (228g) meal of cod once per day and once per week, and to calculate risk using the levels found in this study. If a subsistence fisher from one of the Aleut villages ate one meal of cod per week for As, or one meal per day for Hg, they would exceed the U.S. EPA reference dose for As and Hg (set at a level to be without adverse effect for any person with this average daily exposure).

Coastal coal pollution increases Cd concentrations in the predatory gastropod Hexaplex trunculus and is detrimental to its health

Parameters of environmental health, including paracellular permeability of external epithelia, functional state of lysosomes and the level of metallothioneins (MTs), were examined using fluorescent markers and vital microfluorometry in different tissues of the marine gastropod, Hexaplex trunculus, from a coal-polluted and coal-free site. Vital microfluorometrical examinations exhibited enhanced paracellular permeability of external epithelia to the anionic marker, fluorescein (FLU), lower lysosomal accumulation of neutral red (NR) as well as higher levels of MTs, when compared with epithelia of gastropods from the coal-free site. Those differences were particularly marked in the foot epithelium, which is in direct contact with the substrate. In addition, cadmium was measured by ICP-AES in the hepatopancreas of gastropods sampled from the coal-polluted site and two coal-free sites. Significantly higher levels of Cd were found in gastropod hepatopancreas from the coal-polluted site. In addition, two months feeding experiments conducted in aquaria containing: (a) coal pieces covered by barnacles; (b) natural rocks covered by barnacles; and (c) natural rocks with barnacles + bare coal pieces, demonstrated significant increase of Cd concentration in the hepatopancreas of the gastropods exposed to coal. We suggest that coal in the marine environment has detrimental effects on marine gastropods, both directly through contact with the organisms and indirectly through the food web.