Sequestration of environmental cadmium by metallothionein in the roach (Rutilus rutilus) and the stone loach (Noemacheilus barbatulus)

Two species of coarse fish that are relatively resistant to cadmium poisoning were exposed to sub-lethal concentrations of the metal in their aquarium water. Thus, roach were exposed to cadmium concentrations between 30 and 500 micrograms/l for periods of 14-70 days whereas stone loach were exposed to 1250 micrograms Cd/l for 21-77 days. Under all conditions of exposure, it was found upon analysis of the major organs of accumulation of cadmium in the two species that the toxic metal was sequestered by a single isoform of metallothionein. The amino acid compositions of roach and stone loach metallothionein were determined and found to be similar to those reported for other piscine metallothioneins. The two proteins were found to contain Cd:Zn:Cu in approximate ratios of 4:1:2 per mole of protein. The sequestration of Cd by metallothionein in the two resistant species of fish is contrasted with the situation observed previously in a cadmium-sensitive species, the rainbow trout.     

A comparison of the accumulation and protein binding of environmental cadmium in the gills, kidney and liver of rainbow trout (Salmo gairdneri Richardson)

Rainbow trout were exposed to cadmium in their aquarium water for different lengths of time and at different concentrations. More than 99% of the total body loads accumulated under all such conditions of exposure was found in the liver, kidney and gills. Comparison of the metal-binding proteins in these organs indicated that two low mol. wt proteins sequestered the cadmium while zinc was bound to metallothionein. Cadmium was not found in association with metallothionein unless artificially high concentrations were introduced either by intraperitoneal injection of the fish or by dialysis of tissue extracts in vitro.     

A comparison of the differential accumulation of cadmium in the tissues of three species of freshwater fish, Salmo gairdneri, Rutilus rutilus and Noemacheilus barbatulus

Roach and stone loach were exposed to cadmium dissolved in their aquarium water at 500 and 1250 micrograms/l, respectively, and the distribution of the metal accumulated in the major body organs was determined. The pattern of distribution for each species was somewhat different and was distinct in each case from that observed previously with rainbow trout. The total body loads of cadmium accumulated by the three species were assessed during the period of exposure and found not to correlate directly with the concentration of cadmium to which the individual species had been exposed. An alternative comparator was devised which as the quotient of the total body cadmium accumulation (microgram/100 g body wt) and the notional cadmium dose (microgram/l) X weeks was described as a fractional retention coefficient for cadmium. The coefficient was constant for each species at different periods of exposure to cadmium alone. The values of the coefficient for roach and stone loach were however much lower than that for rainbow trout. When rainbow trout were preexposed to zinc (100 micrograms/l, 5 days) before being exposed to cadmium, the fractional retention coefficient for cadmium fell to a value similar to those seen with roach and stone loach exposed to cadmium alone. The significance of these observations in relation to the nature of the intracellular proteins to which cadmium is bound in the three species is discussed in the light of their differential susceptibility to the toxic effects of cadmium.     

Comparative study on the inhibition of acetylcholinesterase activity in the freshwater fish Cyprinus carpio by mercury and zinc.

The effects of sublethal concentrations of mercury (0.1mg/l) and zinc (6 mg/l) on acetylcholinesterase activity and acetylcholine content of gill, kidney, intestine, brain, liver and muscle of the freshwater fish Cyprinus carpio at 1, 15 and 30 days of exposure were studied. A significant suppression in acetylcholinesterase activity was recorded in all the organs from both mercury and zinc intoxicated fish at all the exposure periods. Concurrently, a significant increase in the content of acetylcholine in the organs was observed. These changes observed in the organs of mercury treated fish in different exposure periods were in the order 1 greater than 15 less than 30 days and in zinc treated fish 1 greater than 15 greater than 30 days. Further, these changes were greater in magnitude in the brain, liver and muscle (non-osmoregulatory organs) than in the gill, kidney and intestine (osmoregulatory organs) in both metal media.     

Cadmium, copper and zinc in tissues of deceased copper smelter workers

Workers at a copper and lead smelter in northern Sweden have a multifactorial exposure to a number of heavy metals. The concentrations of cadmium, copper and zinc in liver, lung, kidney and brain tissues have been determined by atomic absorption spectrometry in 32 deceased long-term exposed male lead smelter workers, and compared with those of 10 male controls. Furthermore, copper and zinc levels in hair and nails were determined by energy-dispersive X-ray fluorescence.

The highest cadmium concentrations among both workers and controls were observed in kidney, followed in order by liver, lung and brain. The levels in kidney, liver and lung were all significantly higher in the workers than in the controls (p < 0.03). Among the workers relatively strong positive correlations (p < 0.03) were observed between cadmium concentrations in liver and lung, liver and kidney, liver and brain, and lung and brain. In the exposed workers a positive correlation was observed between cadmium and zinc concentrations in the kidney (r_s = 0.38; p = 0.034). This is probably mainly due to the protein metallothionein, which is stored in the kidney, binding equimolar amounts of these two metals.

The highest concentrations of copper were found in hair and nails among both workers and controls, followed in order by liver, brain, kidney and lung. The tissue concentrations of copper in brain, lung and kidney were all significantly higher among the smelter workers than in the controls (p ≤ 0.036). Copper levels in lung and age at time of death were positively correlated among the exposed workers (r_s = 0.39; p = 0.029). In the same group, positive correlations between copper and zinc concentrations in kidney (r_s = 0.45; p = 0.009) and nails (r_s = 0.68; p < 0.001) were also observed, reflecting possible biological interactions between these two metals.

Among both workers and controls, the highest zinc concentrations were found in hair, followed in order by nails, liver, kidney, brain and lung. Significantly higher tissue concentrations among the workers as compared with the reference group were noted in kidney, liver and brain (p ≤ 0.033).

Neither copper nor zinc concentrations in hair and nails seemed to provide a useful measure of the trace element status of the smelter workers.     

The effects of cadmium on ALA-D activity, growth and haemoglobin content in the water flea, Daphnia magna

The ALA-D activity, haemoglobin content and growth was studied in the water flea, Daphnia magna, exposed to 0, 0.1, 0.2, 0.4, 0.8 and 1.6 micrograms Cd/l. The ALA-D activity in water fleas exposed to 0.2-1.6 micrograms Cd/l fluctuated around the control value. The activity in animals exposed to 0.1 micrograms Cd/l decreased during the entire experiment. After 16 days exposure to cadmium the haemoglobin content in water fleas ranged between 80 and 31% of control value. In animals exposed to 0.8 and 1.6 micrograms Cd/l the haemoglobin content decreased progressively during the experiment. Growth was not affected by cadmium at these concentrations.     

Metal interactions within and between tissues of nestling rooks Corvus frugilegus

We analyzed interactions of concentrations of 11 essential and nonessential elements, including toxic metals within and between internal organs (liver, kidney and lung), muscles and bones of nestling rooks Corvus frugilegus with acute cadmium contamination and elevated level of lead. The number of statistically significant (P ≤ 0.05) metal-metal relationships (positive/negative) within particular tissues was the highest in the kidney (7/6), following in the bone (9/2), liver (6/4), lung (5/2) and muscle (5/2). We found eight significant interactions of lead with other metals, and only two of cadmium (only with lead and cobalt, which probably mirrored a greater ability of lead (than in the case of cadmium) to functional and kinetic interaction with other metals, and/or inhibiting effect of lead or cadmium in co-accumulation. Furthermore, a positive relationship between concentration of cadmium and lead in the kidney could hint at the key importance of this organ in detoxification of both toxic metals. Analyses of relationships of individual metals between examined tissues show only positive results in the case of copper (n = 8), following potassium (n = 3), zinc and iron (in both cases n = 2) and a single ones for calcium and magnesium. We concluded that the lack of significant relationships of individual toxic metals (cadmium or lead) between analyzed tissues could result from high levels of these metals, which destroyed detoxifying capacity of kidney, and ultimately enabled a rapid bioaccumulation of these inorganic contaminations in all tissues of examined nestlings. An explanation of concentration of toxic metals in tissues of animals, especially in the case of their high level, require an identification of the actual level of essential elements associated with physiological status of organism.     

Environmental and injected cadmium are sequestered by two major isoforms of basal copper, zinc-metallothionein in gibel (Carassius auratus langsdorfi) liver

Gibels were exposed to cadmium in their aquarium at a concentration of 10 micrograms Cd/l for up to 39 weeks. Distributions of cadmium, copper and zinc in the liver soluble fraction were determined along with sulfur by high performance liquid chromatography-inductively coupled argon plasma-atomic emission spectrometry. Cadmium was sequestered by the two major isoforms of gibel metallothionein as in the case of cadmium injected intraperitoneally into gibel. Several peaks with cadmium, copper, zinc and sulfur were observed other than the two major isoforms and their relative ratios were different between the control and cadmium-exposed fishes.     

Effects of lead and lead–melatonin exposure on protein and gene expression of metal transporters,proteins and the copper/zinc ratio in rats

Human lead (Pb) exposure induces many adverse health effects, including some related to lead accumulation in organs. Although lead bio-distribution in the body has been described, the molecular mechanism underlying distribution and excretion is not well understood. The transport of essential and toxic metals is principally mediated by proteins. How lead affects the expression of metal transporter proteins in the principal metal excretory organs, i.e., the liver and kidney, is unknown. Considering that co-administration of melatonin and lead reduces the toxic effects of lead and lead levels in the blood in vivo, we examined how lead and co-administration of lead and melatonin affect the gene and protein expression of metal transporter proteins (ZIP8, ZIP14, CTR1 and DMT1) in these organs. Rats were exposed intraperitoneally to lead or lead-melatonin. Our results show that Pb exposure induces changes in the protein and gene expression of ZIP8, ZIP14 and CTR1. Alterations in the copper/zinc ratio found in the blood, liver and kidney were likely related to these changes. With DMT1 expression (gene and protein), a positive correlation was found with lead levels in the kidney. Co-administration of melatonin and lead reduced lead-induced DMT1 expression through an unknown mechanism. This effect of melatonin relates to reduced lead levels in the blood and kidney. The metal transport protein function and our results suggest that DMT1 likely contributes to lead accumulation in organs. These data further elucidate the effects of lead on Cu and Zn and the molecular mechanism underlying lead bio-distribution in animals.     

Role of metallothioneins in metal regulation by the guillemot Uria aalge

Guillemots, like other seabird species living in the North Sea, appear to be heavily contaminated by copper. Metallothioneins are present in both liver and kidney but, at least in the specimens stranded along the Belgian coast, fail to maintain constant the copper, zinc and cadmium load of the high molecular weight soluble proteins of both organs, stressing the potential toxic role of these metals, mainly copper.     

Zinc,cadmium, mercury and selenium in minke whales,belugas and narwhals from West Greenland

Summary Samples of muscle, liver and kidney from 24 minke whales (Balaenoptera acutorostrata), 43 belugas (Delphinapterus leucas), and 98 narwhals (Monodon monoceros) were analyzed for zinc, cadmium, mercury, and selenium. Highly significant age accumulation of mercury was found. A lower level of significance of age accumulation of cadmium in belugas and narwhals is probably due to the fact that some of the highest cadmium concentrations are in subadults and young adults. The maximum concentrations of cadmium and mercury are very high: 1.68, 73.7, and 125 g cadmium, and 9.88, 42.8, and 4.61 g mercury per g wet weight of narwhal muscle, liver and kidney, respectively. The cadmium concentrations are correlated in the three organs, as are mercury and to a lesser extent selenium concentrations. The concentrations of mercury and selenium in liver are highly correlated.     

Low iron diet and parenteral cadmium exposure in pregnant rats: the effects on trace elements and fetal viability

The effects of latent iron deficiency combined with parenteral subchronic or acute cadmium exposure during pregnancy on maternal and fetal tissue distribution of cadmium, iron and zinc, and on fetal viability were evaluated. Timed-pregnant Sprague-Dawley rats were fed on semisynthetic test diets with either high iron (240 mg kg) or low iron (10 mg kg), and concomitantly exposed to 0, 3 or 5 mg cadmium (as anhydrous CdCl₂) per kilogram body weight. Animals were exposed to cadmium from gestation day 1 through 19 by subcutaneously implanted mini pumps (Subchronic exposure) or on gestation day 15 by a single subcutaneous injection (Acute exposure). All rats were killed on gestation day 19. Blood samples, selected organs and fetuses were removed and prepared for element analyses by atomic absorption spectrometry. Low iron diet caused decreases in maternal body weight, maternal and fetal liver weights, placental weights and tissue iron concentrations. By cadmium exposure, both subchronic and acute, tissue cadmium concentrations were increased and the increase was dose-related, maternal liver and kidney zinc concentrations were increased, and fetal zinc concentration was decreased. Cadmium concentration in maternal liver was additionally increased by low iron diet. Acute cadmium exposure caused lower maternal body and organ weights, high fetal mortality, and decreased fetal weights of survivors. In conclusion, parenteral cadmium exposure during pregnancy causes perturbations in essential elements in maternal and fetal compartments. Acute cadmium exposure in the last trimester of gestation poses a risk for fetal viability especially when combined with low iron in maternal diet.     

Use of the fish enzyme system in monitoring water quality: effects of mercury on tissue enzymes

1. Rosy barb (Puntius conchonius) were exposed to 181 micrograms/l mercuric chloride for 48 h and the activity of acid and alkaline phosphatases (AcP and AIP), aspartate aminotransferase (AAT), alanine aminotransferase (AIAT), lactic dehydrogenase (LDH), and acetylcholinesterase (AchE) were measured in vivo in several organs. 2. The AcP activity was inhibited in the liver, gills, kidneys, and gut but stimulated in the gonads. With the exception of kidney, the AIP activity showed an increase in all the organs examined. The AAT and AIAT were generally inhibited in different organs. An increase in LDH activity occurred in the cardiac and skeletal muscles while the AchE activity was considerably lowered in the brain, gills, and liver. 3. In vitro exposure to mercury at concentrations ranging between 10(-10) and 10(-4) M, inhibited the AIP, AAT, AIAT, LDH, and AchE activities in the tissues examined. The AcP activity was also depressed in all the tissues except in the testes, in which a marginal increase was noted. 4. The in vivo and in vitro effects of Hg were not of similar quality implying sequestration of toxic cations in the intact animals.     

Ultrastructural biomarkers as tools to characterize the health status of fish in contaminated streams

Ultrastructural biomarkers in gill, liver, andkidney of brown trout (Salmo truttaf. fario) and stone loach (Barbatulabarbatula) were investigated over afive year period. The cellular damage of theorgans was assessed semi-quantitatively basedon a three-step classification ofultrastructural responses. Data obtained forfish exposed under semi-field conditions in twodifferently polluted test streams and in thelaboratory demonstrated that the ultrastructureof the organs can be correlated with differentpollutant exposure conditions. Cellular damagewas generally more severe in fish exposed to acomplexly polluted stream than in those exposedto a moderately polluted stream or to tap waterin the laboratory. Histopathological effects inliver and gill of trout were more pronounced inferal fish than in transplanted fish, whereasresponses in the kidney in both species, and inliver and gill of loach, were similar forintroduced and feral fish. In a laboratoryexperiment where trout were exposed todifferent mixtures of pollutants includingpesticides, PAH, and ammonia, only theultrastructure of kidney and liver showedsignificant differences between the threeexperimental set-ups. In a recovery experiment,where trout were transferred from thesemi-field condition back to the laboratory,ultrastructural investigations showed adifferential capacity of the respective organsto recover from stress under field conditions.Kidney and liver fully recovered after threemonths under control condition whereas gillsdemonstrated only partial recovery.     

Effects of cadmium administration on the endogenous metal balance in rats

The concentrations of cadmium and other metal ions in selected organs, urine, and blood of female rats were measured after exposure to cadmium chloride through their diet or by oral or intravenous administration. The hematological and urinary variations were followed for 4 wk. Body weight gain and the weights of livers and kidneys from all treated groups were not significantly different from the controls. No gross morphological changes were observed in any of the tissues studied at necropsy. The accumulation of cadmium occurred in the liver and kidney. The zinc levels in these organs were elevated relative to controls, in all treated groups regardless of dose and exposure route. Copper was elevated in the liver, kidney, bone, and blood of animals subject to intravenous administration of cadmium. Hepatic iron was decreased in the dietary and orally treated groups, but was not affected in the intravenous study group. The level of magnesium in kidney was increased for all exposure routes, but that of liver was increased only in the intravenously injected groups. The changes in the concentrations of sodium, potassium, calcium, and phosphorus did not follow a specific pattern and varied from organ to organ, depending on the exposure route. The discussion includes a relationship between tissue injury and the alteration of tissue essential element concentrations.     

Soft-tissue accumulation of lead in the blue tilapia,Oreochromis aureus (steindachner), and the modifying effects of cadmium and mercury

The interaction of mercury and cadmium with lead was investigated by exposingOreochromis aureus to two heavy metals simulataneously. The chronic accumulation prolife of lead was determined by analyzing the liver, brain, gill filaments, intestine, caudal muscle, spleen, trunk kidney, and gonads following exposure to lead alone and in mixtures with mercury and cadmium. Nominal exposure concentrations of lead were 0.05, 0.10, 0.50, and 1.00 mg/L. Mixtures of lead (0.50 or 0.05 mg/L) with cadmium (0.05 mg/L) and lead (0.50 or 0.05 mg/L) with mercury (0.05 mg/L) were also used. Following 140 d of exposure to lead, the highest concentrations of lead consistently accumulated in the trunk kidney. The concentration of lead in the kidney was decreased by coexposure to mercury or cadmium, but increased in the muscle and liver. Under all exposure regimes, the median concentration of lead in the muscle exceeded safety levels recommended for human consumption. In a food fish, such asO. aureus, a knowledge of toxic metal accumulation patterns is of great importance.     

Comparative distributions of zinc, cadmium and mercury in the tissues of experimental mice

Different groups of mice were injected with cadmium, zinc and mercury. Zinc injections had no effect on zinc tissue levels while both mercury and cadmium accumulated in various tissues. Cadmium persisted in the tissues much longer than mercury, and while the mercury concentrations began to decline as soon as dosing ceased, cadmium concentrations in kidney and intestine increased even after dosing ceased. There appeared to be an interrelationship between cadmium concentrations in spleen and intestine which warrants some further investigations. There was a linear, but discontinuous, effect of cadmium on zinc concentrations in liver, kidney and pancreas which may depend on metallothionein biochemistry. Mercury injections had no effect on zinc metabolism. It is proposed that differences in the rate of excretion of cadmium and mercury from the kidney could explain the differential accumulation of cadmium and mercury in animals.     

Cadmium and copper contents in a freshwater fish species (brook trout, Salvelinus fontinalis) from the subantarctic Kerguelen Islands

The subantarctic Kerguelen Islands (49°S, 70°E) contain freshwaters among the most isolated in the world from direct human activities. Cadmium and copper concentrations were analyzed in muscle and liver tissues of 57 non-migratory brook trout (Salvelinus fontinalis) inhabiting the Sud River of Kerguelen Islands. The mean cadmium concentration in liver was 1.13 μg/g dry wt, within the range of levels measured in liver of marine fish from the Southern Ocean. Muscular Cd levels (0.12 μg/g dry wt) were roughly ten times higher than those measured in Kerguelen’s marine fish species. Copper levels were very high in the two organs (62.27 μg/g dry wt in liver and 3.02 μg/g dry wt in muscle) compared to those detected in fish from the Southern Ocean. Regarding the seasonal trend, the highest Cu and Cd muscular levels were measured in fish at the end of the austral winter, whereas the highest hepatic levels were observed at the end of the austral summer. Moreover, hepatic cadmium levels were higher in females than in males. These results could be related to brook trout spawning physiological preparations and foraging behavior during the summer period. We provide here the first results about Cu and Cd levels in liver and muscle of a freshwater fish species in an insular subantarctic context. They are in agreement with the high cadmium contamination found in fish of the Southern Ocean.     

Influence of dietary cadmium on the distribution of the essential metals copper,zinc and iron in tissues of the rat

The effect of long-term dietary cadmium treatment upon the distribution of the metals copper, iron and zinc has been compared in various organs of male and female rats. The renal accumulation of cadmium was similar in both sexes without a plateau being reached. In contrast, the hepatic accumulation of cadmium was higher in the female than in the male rat and a plateau was observed after 30–35 weeks of dietary cadmium treatment. Most of the cadmium which accumulated in these organs was recovered in the metallothionein fraction and the concentration of hepatic cadmiumthionein in the female rat was correspondingly higher than in the male rat. Accumulation of cadmium was associated with an increased zinc concentration in the liver and an increased copper concentration in the kidney; these increases were correlated with increases in liver and kidney metallothioneins induced by cadmium. Uptake of cadmium into organs other than liver and kidney occurred to a small extent but was not associated with changes in the concentration of copper and zinc. Cadmium also accumulated in the intestinal mucosa where it could be recovered in a fraction corresponding to metallothionein. A loss of iron from the liver and kidney was also observed following dietary cadmium treatment and involved mainly a loss of iron from ferritin.     

Chronological changes in tissue copper, zinc and iron in the toxic milk mouse and effects of copper loading

The toxic milk (tx) mouse is a rodent model for Wilson disease, an inherited disorder of copper overload. Here we assessed the effect of copper accumulation in the tx mouse on zinc and iron metabolism. Copper, zinc and iron concentrations were determined in the liver, kidney, spleen and brain of control and copper-loaded animals by atomic absorption spectroscopy. Copper concentration increased dramatically in the liver, and was also significantly higher in the spleen, kidney and brain of control tx mice in the first few months of life compared with normal DL mice. Hepatic zinc was increased with age in the tx mouse, but zinc concentrations in the other organs were normal. Liver and kidney iron concentrations were significantly lower at birth in tx mice, but increased quickly to be comparable with control mice by 2 months of age. Iron concentration in the spleen was significantly higher in tx mice, but was lower in 5 day old tx pups. Copper-loading studies showed that normal DL mice ingesting 300 mg/l copper in their diet for 3 months maintained normal liver, kidney and brain copper, zinc and iron levels. Copper-loading of tx mice did not increase the already high liver copper concentrations, but spleen and brain copper concentrations were increased. Despite a significant elevation of copper in the brain of the copper-loaded tx mice no behavioural changes were observed. The livers of copper-loaded tx mice had a lower zinc concentration than control tx mice, whilst the kidney had double the concentration of iron suggesting that there was increased erythrocyte hemolysis in the copper-loaded mutants.