Effects of chronic Cd exposure via the diet or water on internal organ-specific distribution and subsequent gill Cd uptake kinetics in juvenile rainbow trout (Oncorhynchus mykiss)

Cadmium-109 Internal Kinetics in Diamond Sturgeon Acipenser gueldenstaedtii are Strongly Influenced by Salinity, Exposure Pathway and History

Cadmium-109 whole-body and internal biokinetics were experimentally investigated in critically endangered diamond sturgeon Acipenser gueldenstaedtii after uptake from water or food, in fresh (FW) and brackish (BW; 9‰) salinities typical of the Caspian Sea. Whole-body rates of uptake of 109Cd from water and subsequent depuration were quantified over 14 and 28 days, respectively. Uptake was greater in FW than BW by a factor of 2.4, but depuration rates were similar in both salinities. In contrast, for the dietary (chironomid) exposure pathway 109Cd assimilation efficiencies (AEs) were higher in BW (13%) compared to FW (9.5%). Head (including gills) or digestive tract were major repositories of 109Cd following aqueous and dietary exposures, respectively, including both uptake and depuration phases. The point-of-entry of 109Cd into the body was also a major and persistent determiner of its subsequent internal distribution. For aqueous exposures, the internal distributions of 109Cd changed appreciably during depuration with increased activity concentrations in some body components, which again varied with salinity. Increased salinity appreciably enhanced the percentage distributions and activity concentrations of 109Cd in the liver, kidney and digestive tract, which are typically most pathologically altered by elevated Cd exposure. For dietary exposure, increased salinity also enhanced 109Cd activity concentrations in most body components. The results repeatedly indicate the important role of salinity in the whole-body and internal biokinetics of 109Cd in A. gueldenstaedtii, a representative of both a phylogenetically distinct and most endangered family of fishes.

Temperature Effects During a Sublethal Chronic Metal Mixture Exposure on Common Carp (Cyprinus carpio)

The aquatic environment is the final sink of various pollutants including metals, which can pose a threat for aquatic organisms. Waterborne metal mixture toxicity might be influenced by environmental parameters such as the temperature. In the present study, common carp were exposed for 27 days to a ternary metal mixture of Cu, Zn, and Cd at two different temperatures, 10 and 20°C. The exposure concentrations represent 10% of the 96 h-LC₅₀ (concentration lethal for the 50% of the population in 96 h) for each metal (nominal metal concentrations of Cu: 0.08 μM; Cd: 0.02 μM and Zn: 3 μM). Metal bioaccumulation and toxicity as well as changes in the gene expression of enzymes responsible for ionoregulation and induction of defensive responses were investigated. Furthermore the hepatosomatic index and condition factor were measured as crude indication of overall health and energy reserves. The obtained results showed a rapid Cu and Cd increase in the gills at both temperatures. Cadmium accumulation was higher at 20°C compared to 10°C, whereas Cu and Zn accumulation was not, suggesting that at 20°C, fish had more efficient depuration processes for Cu and Zn. Electrolyte (Ca, Mg, Na, and K) levels were analyzed in different tissues (gills, liver, brain, muscle) and in the remaining carcasses. However, no major electrolyte losses were observed. The toxic effect of the trace metal ion mixture on major ion uptake mechanisms may have been compensated by ion uptake from the food. Finally, the metal exposure triggered the upregulation of the metallothionein gene in the gills as defensive response for the organism. These results, show the ability of common carp to cope with these metal levels, at least under the condition used in this experiment.

Comparative and Interactive Biochemical Effects of Sub-Lethal Concentrations of Cadmium and Lead on Some Tissues of the African Catfish (Clarias gariepinus)

Cadmium is a strong toxic heavy metal which presents in paints and liquid wastes and causes oxidative stress in fish. On the other hand, lead is widely used for different purposes, e.g. lead pipes, it targets vital organs such as liver and kidney causing biochemical alterations. The present study evaluates the effects of 60 days exposure to Cd and Pb either single or combined together in African catfish. Sixty-four fishes were divided into 3 groups and exposed to CdCl2 (7.02 mg/L) or PbCl2 (69.3 mg/L) or a combination of them along with control group. Activities of acid phosphatase (ACP), lactate dehydrogenase (LDH) and glucose-6-phosphate dehydrogenase (G-6-PDH) were estimated. Moreover, gill, liver and kidney were assayed for activities of superoxide dismutase (SOD), catalase (CAT) and levels of glutathione (GSH) and malondialdehyde (MDA). Individual exposure showed that both Cd and Pb significantly decreased LDH activity and SOD activity in the kidney. Pb significantly increased G-6-PDH activity and decreased GSH level in the gill. CAT activity in liver and kidney elevated significantly on Cd exposure while lead caused a significant depletion in the liver and significant elevation in the kidney. Both Cd and Pb significantly increased MDA levels in liver and kidney while Pb increased its level in gills. The combined exposure resulted in normalization of LDH, G-6-PDH activity, and CAT activity in liver and kidney as well as GSH level in both tissues and MDA in gill and kidney. The combination increased SOD activity and MDA level in liver and decreased SOD activity in kidney and GSH level in gills. In conclusion, the antioxidant system of African catfish was adversely affected by prolonged exposure to Cd and Pb. The combined exposure caused less damage than individual exposure and returned most parameters to those of controls.

Effects of exposure to multiple heavy metals on biochemical and histopathological alterations in common carp, Cyprinus carpio L

Heavy metals are frequently encountered as mixtures of essential and non-essential elements. Therefore, evaluation of their toxic effects individually does not offer a realistic estimate of their impact on biological processes. We studied effects of exposure to mixtures of essential and toxic metals (Cr, Cd and Pb) on biochemical, immunotoxicity level and morphological characteristics of the various tissues of a biomarker freshwater fish common carp using environmentally relevant concentrations. Fish were exposed to metal mixture through tank water for 7, 15 and 30 days, under controlled laboratory conditions. Tissue accumulation of the metals was measured using Atomic Absorption Spectrophotometric techniques. Chromium, cadmium and lead accumulation in muscle, gills, liver, kidney and intestine, tissue of common carp exposed to mixture metals for 30 days increased significant compared with control group (p < 0.001). However, the activity of antioxidant enzymes such as catalase (CAT) and superoxide dismutase (SOD) levels was significant altered in various tissues of exposed fish. Besides, the lipid peroxidation (LPO) was significant (p < 0.001) increased. Moreover, the tumor necrosis factor - α (TNF-α), interleukin (IL-6), and interferon-γ (IFN-γ) contents in tissues of muscle, gills, liver, kidney and intestine were increased significant compared with control fish (p < 0.001). In addition, microscopic examination of the main alterations in general morphology of fish gills included spiking and fusion of secondary lamellae, formation of club-shaped filaments epithelium in the interlamellar regions and hepatocytes showed damage of central vein and rupture of irregular hepatic plate with more number of vacuoles in the fish exposed to metal mixture for a longer duration (30 days). These results of this study clearly demonstrate that concentration individual and mixtures of metals in aquatic systems will greatly influence the cytokine alterations may result in an immune suppression or excessive activation in the treated common carp as well as may cause immune dysfunction or reduced immunity. In conclusion, toxicity of multiple metal mixtures of Cr, Cd and Pb has antioxidant and immunotoxic effects on C. carpio.

Effects of Different Dietary Cadmium Levels on Growth and Tissue Cadmium Content in Juvenile Parrotfish, Oplegnathus fasciatus

This feeding trial was carried out to evaluate the effects of different dietary cadmium levels on growth and tissue cadmium content in juvenile parrotfish, Oplegnathus fasciatus, using cadmium chloride (CdCl₂) as the cadmium source. Fifteen fish averaging 5.5±0.06 g (mean±SD) were randomly distributed into each of twenty one rectangular fiber tanks of 30 L capacity. Each tank was then randomly assigned to one of three replicates of seven diets containing 0.30 (C₀), 21.0 (C₂₁), 40.7 (C₄₁), 83.5 (C₈₃), 162 (C₁₆₂), 1,387 (C_1,387) and 2,743 (C_2,743) mg cadmium/kg diet. At the end of sixteen weeks of feeding trial, weight gain (WG), specific growth rate (SGR) and feed efficiency (FE) of fish fed C₂₁ were significantly higher than those of fish fed C₈₃, C₁₆₂, C_1,387 and C_2,743 (p<0.05). Weight gain, SGR and FE of fish fed C₀, C₂₁ and C₄₁ were significantly higher than those of fish fed C₁₆₂, C_1,387 and C_2,743. Protein efficiency ratio of fish fed C₀, C₂₁ and C₄₁ were significantly higher than those of fish fed C_1,387 and C_2,743. Average survival of fish fed C₀, C₂₁, C₄₁ and C₁₆₂ were significantly higher than that of fish fed C_2,743. Tissue cadmium concentrations increased with cadmium content of diets. Cadmium accumulated the most in liver, followed by gill and then muscle. Muscle, gill and liver cadmium concentrations of fish fed C₀, C₂₁, C₄₁ and C₈₃ were significantly lower than those of fish fed C₁₆₂, C_1,387 and C_2,743. Based on the ANOVA results of growth performance and tissue cadmium concentrations the safe dietary cadmium level could be lower than 40.7 mg Cd/kg diet while the toxic level could be higher than 162 mg Cd/kg diet.

Ultimobranchial gland of a freshwater teleost, Heteropneustes fossilis, in response to cadmium treatment

Heteropneustes fossilis were subjected to 288 mg/L (0.8 of 96 h LC(50)) and 72 mg/L (0.2 of 96 h LC(50)) of cadmium chloride for short-term and long-term experiments, respectively. After sacrificing the fish, the blood was collected on 24, 48, 72, and 96 h in short-term and after 7, 14, 21, and 28 days in long-term experiment and analyzed for plasma calcium levels. Also, ultimobranchial glands were fixed on these intervals. The plasma calcium levels of short-term cadmium-exposed fish remain unchanged after 24 h. The levels exhibit a progressive decrease from 48 h onwards. The fish exposed to cadmium for 7 days exhibit a decrease in the plasma calcium level. Thereafter, the levels progressively decrease till the end of the experiment (28 days). Up to 72 h exposure of the fish to cadmium, the ultimobranchial gland exhibits no histological change. After 96 h, a decrease in the staining response of the cytoplasm of ultimobranchial cells has been noticed. The nuclear volume of these cells records a slight decrease. Up to 14 days of cadmium exposure, there is no change in the histological structure of ultimobranchial gland. After 21 days following the exposure, the ultimobranchial cells exhibit a slight decrease in the staining response of the cytoplasm and the nuclear volume of these cells records a decrease. Following 28 days cadmium exposure the nuclear volume exhibits a further decrease, and degeneration and vacuolization sets in.

Kinetics of cadmium uptake and subcellular partitioning in the earthworm Eisenia fetida exposed to cadmium-contaminated soil

To understand the bioaccumulation kinetics of cadmium (Cd) at the subcellular level, toxicokinetics and subcellular fractionation of Cd were determined for the terrestrial earthworm Eisenia fetida exposed to Cd-contaminated red soil. The bioaccumulation factor was 1.74 after exposure to soil containing 1 mg Cd/kg dry weight for 21 days. Four distinct compartments with different Cd-binding affinities were obtained by sequential centrifugations, including the cytosolic fraction (G), the organelles fraction (F), the granular fraction (D), and the tissue, cell membrane, and intact cell fraction (E). Most of the accumulated Cd in the organisms existed as fraction G. Cd bound to the tissue and cell membrane fraction (E) was <8% of total Cd. Only approximately 3% of Cd existed in fraction F, and <1% was found in fraction D. Accumulation and elimination kinetics of Cd in different fractions were accurately described by one-compartment models, and kinetic parameters (uptake rate constant k ( 1 ) and elimination rate constant k ( 2 )) were derived. Fractions G and F were responsible for the linear accumulation pattern during 3 weeks of exposure, whereas fractions D and E showed a nonlinear uptake curve, and steady state was achieved after 7 and 14 days of exposure, respectively.

Can thiol compounds be used as biomarkers of aquatic ecosystem contamination by cadmium?

Due to anthropogenic activities, heavy metals still represent a threat for various trophic levels. If aquatic animals are exposed to heavy metals we can obviously observe considerable toxicity. It is well known that an organism affected by cadmium (Cd) synthesize low molecular mass thiol compounds rich in cysteine (Cys), such as metallothioneins (MT) and glutathione (GSH/GSSG). The aim of this study was to summarize the effect of Cd on level of thiol compounds in aquatic organisms, and evaluate that the concentrations of thiol compounds are effective indicators of Cd water pollution and explain their potential use in biomonitoring applications.

Protective effect of high alkalinity against the deleterious effects of chronic waterborne cadmium exposure on the detection of alarm cues by juvenile silver catfish (Rhamdia quelen)

The objective of the present study was to analyze the effect of chronic cadmium (Cd) exposure at two alkalinity levels (63 and 92 mg l(-1) CaCO(3)) on the antipredatory behavior of juvenile silver catfish (Rhamdia quelen) exposed to conspecific skin extract and predator odor. At an alkalinity of 63 mg l(-1) CaCO(3), 30 days of exposure to either 4.5 or 8.0 microg l(-1) Cd impaired the catfish's antipredatory response to alarm cues. However, silver catfish exposed to 4.5 microg l(-1) Cd at an alkalinity of 92 mg l(-1) CaCO(3) responded to skin extract and predator odor. In catfish exposed to 8.0 microg l(-1) Cd at the same alkalinity, only the number of feeding bites decreased, and this occurred only for specimens exposed to predator odor. Our results show that higher alkalinity protected against the deleterious effects of Cd on alarm cue detection but only in the larvae exposed to the lowest waterborne Cd level.

A biotic ligand model-based toxicodynamic approach to predict arsenic toxicity to tilapia gills in cultural ponds

Farming of tilapia Oreochromis mossambicus is an important aquacultural activity in Taiwan. Due to the elevated arsenic (As) concentration in pond water, it is important to assess the bioavailability and toxicity of As to tilapia for protection of aquatic life and human health. In the present study, we developed a biotic ligand model (BLM)-based toxicodynamic approach to dynamically predict both acute and chronic effective concentrations of As to tilapia in two tilapia farms located at Pudai and Chiangchun counties in southwestern Taiwan. Parameters revealed in the mechanistic model were obtained by fitting this model to the toxicokinetic and toxicodynamic data from our previous laboratory experiments. Based on our extended BLM concepts, the site-specific water effect ratios and ambient water quality criteria can be determined with known water chemistry. The proposed methodology was capable of bridging the gap between laboratory toxicity bioassays and field investigations. With respect to risk assessments, our research may also provide an useful means of generating and adjusting the site-specific ambient water quality criteria.

Metal-specific interactions at the interface of chemistry and biology

Metals have complex environmental chemistry. When metals are present at elevated levels, they cause toxicity. Some metals are essential for living organisms, and those metals occur naturally in the environment. The latter aspect has allowed biological species to adapt to long- and short-term variations in metal levels. Chemical speciation, bioavailability, bioaccumulation, toxicity, and mixture effects are key issues in assessing the hazards of metals.

In the present contribution, a global overview is given of the interactions between the chemistry and biology of metals, mostly at the interface of biological and environmental matrices. The environmental chemistry of metals and resulting methods for assessing metal availability are assumed as tokens, and the emphasis is thus on biological processes affecting the fate and effects of metals following interaction of the organism with the bioavailable metal fraction. The overview culminates in linking metal compartmentalization in organisms to bioaccumulation and toxicity.

Tissue-specific cadmium and metallothionein levels in rainbow trout chronically acclimated to waterborne or dietary cadmium

Rainbow trout were exposed to a sublethal concentration of waterborne Cd (0 or 3 microg/L) or dietary Cd (0 or 500 mg/kg dry wt) for 30 days to induce acclimation, and tissue Cd and metallothionein (MT) levels were examined. The greatest Cd concentrations were observed in the kidney followed by the gills and liver of the fish exposed to Cd via water, but in the gut tissues followed by the kidney, liver, and gills for dietary-exposed fish, reflecting a variation depending on the route of Cd exposure. Some MT was found in the nonacclimated naïve fish with no experience of elevated Cd exposure, and these background MT levels were quite high in the posterior intestine (480 microg/g), cecae (257 microg/g), and liver (248 microg/g) relative to other tissues (7-50 microg/g). With exposure to both waterborne and dietary Cd, MT levels rose significantly in all observed tissues. The increases relative to the control levels of MT in naïve fish were in the order: kidney (5.4 times) > gills (4.6) > liver (1.3) for the waterborne exposure group, and in the order kidney (19.3 times) >> cecae and posterior intestine (approximately 6.5 times) > liver and stomach (approximately 5 times) > midintestine (4.3 times) > gills (2.1 times) for the dietary exposure group. At 24 hours after an acute gastrointestinal dose of Cd (276 microg/kg) infused into the stomach of dietary exposure groups, large increases of total Cd but not MT levels were found in the gut tissues of nonacclimated fish; in the Cd-acclimated fish, the posterior intestine was greatly affected with decreases in Cd (71%), Zn (33%), Cu (70%) and MT (46%) levels, suggesting an enhanced sloughing of tissue materials after infusion. Exposure to Cd did not cause any notable decrease of Zn or Cu in any tissue, except that found in the posterior intestine. However, a molar analysis indicated that although Cd levels remained less than MT binding capacity in both waterborne and dietary exposure groups, the total metal levels (Cd + Zn + Cu) greatly exceeded MT binding capacity in all tissues of Cd-exposed fish, suggesting a potential competition of Cd with other metals for binding sites on MT and non-MT proteins in the tissues.