Relations between liver cadmium, cumulative exposure, and renal function in cadmium alloy workers.

Detailed biochemical investigations of renal function were made on 75 male workers exposed to cadmium and an equal number of referents matched for age, sex, and employment status. The exposed group consisted of current and retired workers who had been employed in the manufacture of copper-cadmium alloy at a single factory in the United Kingdom for periods of up to 39 years and for whom cumulative cadmium exposure indices could be calculated. In vivo measurements of liver and kidney cadmium burden were made on exposed and referent workers using a transportable neutron activation analysis facility. Significant increases in the urinary excretion of albumin, retinol binding protein, beta 2 microglobulin, N-acetylglucosaminidase (NAG), alkaline phosphatase, gamma-glutamyl transferase and significant decreases in the renal reabsorption of calcium, urate, and phosphate were found in the exposed group compared with the referent group. Measures of glomerular filtration rate (GFR) (creatinine clearance, serum creatinine, and beta 2 microglobulin) indicated a reduction in GFR in the exposed population. Many of these tubular and glomerular function indicators were significantly correlated with both cumulative exposure index and liver cadmium burden. Using cumulative exposure index and liver cadmium as estimates of dose, a two phase linear regression model was applied to identify an inflection point signifying a threshold level above which changes in renal function occur. Many biochemical variables fitted this model; urinary total protein, retinol binding protein, albumin, and beta 2 microglobulin gave similar inflection points at cumulative exposure levels of about 1100 y.micrograms/m3 whereas changes in the tubular reabsorption of urate and phosphate occurred at higher cumulative exposure indices. Measures of GFR, although fitting the threshold model did not give well defined inflection points. Fewer variables fitted the two phase model using liver cadmium; those that did gave threshold levels in the range 20.3-55.1 ppm. When cadmium workers with cumulative exposure indices of less than 1100 y.micrograms/m3 were compared with their respective referents only serum beta 2 microglobulin and urinary NAG were significantly increased in the exposed group and these differences were not related to the degree of cadmium exposure.(ABSTRACT TRUNCATED AT 400 WORDS)     

镉毒性肾损害与镉、锌结合蛋白——Ⅰ.尿金属硫蛋白对镉毒性肾损害的检测价值

采用Sephadex G-75凝胶柱色谱技术对亚急性镉毒性肾损害大鼠肝、肾、血、尿中金属硫蛋白(MT)进行了分离测定。结果表明,镉暴露后,肝、肾、血、尿中MT增多。MT是体内镉的主要存在形式,其在体内镉的运转、蓄积及排泄过程起最重要的作用。尿中MT增高是镉毒性肾损害最早出现的变化之一,它作为低分子蛋白质是肾小管功能障碍的灵敏指标。同时,作为一种镉金属结合蛋白,在反映镉性肾损害有其特异性。     

Phytoextraction and phytoexcretion of Cd by the leaves of Tamarix smyrnensis growing on contaminated non-saline and saline soils

Phytoremediation and more specifically phytoextraction, is an alternative restoration strategy for the clean up of heavy metal contaminated soils. Phytoextraction can only be successful if suitable plant species colonize the contaminated area, extract the toxic substances and accumulate them in their above ground tissues. In this study, the salt cedar Tamarix smyrnensis that is a widespread salt-tolerant plant in the Mediterranean region has been investigated. A pot experiment is conducted with T. smyrnensis grown in polluted soil with 16ppm of cadmium and at three different salt concentrations (0.0, 0.5, 3.0% NaCl) for a 10-week period. It took place in an open-air area with natural light, at ambient temperature and humidity in an effort to keep the plants under conditions as similar as possible to those in the field. However, care was taken not to let them be rained on. Temperature ranged from 19 to 50 degrees C with 33 and 21 degrees C being the average day and night temperature, respectively. Humidity ranged from 28% to 87% with a 13-14h photoperiod. The specific aims of this work are to investigate the accumulation of cadmium via root uptake at different saline conditions and cadmium excretion through salt glands on the surface of the leaves as a probable detoxification mechanism of the plant. Furthermore, measurements of chlorophyll content, biomass, and shoot length are used to evaluate the potential of the plant for the removal of cadmium from contaminated saline and non-saline soils. The experimental data suggest that increased soil salinity results in an increase of the cadmium uptake by T. smyrnensis. Analysis of white salt crystals taken from glandular tissue confirmed the fact that this plant excretes cadmium through its salt glands on the surface of the leaves as a possible detoxification mechanism in order to resist metal toxicity. Excreted cadmium is again released into the environment and it is redeposited on the top soil. Furthermore, increased salinity results in an increased excretion of the metal on Tamarix leaf surface. The presence of metals usually affects negatively the plant health, but T. smyrnensis developed no visible signs of metal toxicity, only salt toxicity symptoms were observed. Cadmium usually decreases the chlorophyll content in plants; however, the amount of photosynthetic pigments of T. smyrnensis was found not to be affected. All the above points to the potential of T. smyrnensis for use in phytoremediation with the metal secretion from the leaves being a unique advantage that may change current phytoextraction practices.     

Cadmium Interaction with Essential Metals (Zn, Cu, Fe), Metabolism Metallothionein, and Ceruloplasmin in Pregnant Rats and Fetuses

Cadmium administered to rats per os is accumulated in the duodenal mucosa in the form of metallothionein (MT). Therefore, this toxic metal can influence the efficiency of essential metal absorption, especially their concentration in the maternal organism, which plays an essential role during fetal development. The aim of this study is to elucidate the mechanism of the origin of Zn, Cu, and Fe deficiency in fetal rat livers after maternal exposure to cadmium in drinking water and to investigate the roles of MT and ceruloplasmin (Cp) in this phenomenon. Cadmium was given to pregnant dams exposed for 0–20 days of gestation in drinking water at concentrations of 6.25–100 μg Cd/ml. After cessation of exposure, at the lowest dose, a decrease in Cu and Fe concentrations in the duodenal mucosa was found. Simultaneously, diminution in concentration of two cited metals and Cp activity in serum of dam blood was noted. The lowest dose of cadmium developed a drop tendency in microsomal fetal liver iron. Significant correlations were observed between fetal liver Cu contents and Cp activity in serum of dams and Cu concentrations in serum of dams. Diminished Cp activity in serum of dams is related to reduced availability of Cu and Fe in fetuses. In conclusion, it is suggested that the mechanism of Cu and Fe deficit content in fetuses is based on the diminution of absorption of these metals by dam intestines exposed to cadmium on the reduction of metal concentrations in blood serum and, in consequence, their decreasing availability in fetuses.     

Cadmium Accumulation in Gill,Liver, Kidney and Muscle Tissues of Common Carp,Cyprinus carpio,and Nile Tilapia,Oreochromis niloticus

Accumulation of cadmium in gill, liver, muscle and kidney tissues of Cyprinus carpio and Oreochromis niloticus were investigated in fish exposed to 0.5 ppm cadmium over 1, 15 and 30 days under controlled laboratory conditions. Tissue accumulation of the metal was measured using Atomic Absorption Spectrophotometric techniques. Cadmium accumulation in gill, liver, kidney and muscle, tissues of C. carpio and O. niloticus exposed to metal for 1, 15 and 30 days increased significantly compared with the control group (p < 0.05), except muscle tissue of O. niloticus. A general increase was observed in Cd accumulation with increasing exposure periods. Highest metal accumulation was observed in kidney followed by liver, gill and muscle tissues in both species. Liver accumulation of Cd was higher in C. carpio than O. niloticus, whereas kidney accumulation of the metal was higher in O. niloticus than C. carpio.     

The effect of dietary zinc status on biliary metal excretion of rats

The effect of dietary zinc status on biliary excretion of zinc, cadmium and mercury administered as a bolus of metal chloride (1 mg metal/kg body weight i.v.) was studied. Female rats were fed a purified diet containing either 9 micrograms/g (low), 45 micrograms/g (adequate) or 1150 micrograms/g (high) zinc for 8 d. Hepatic metallothionein (MT) was similar in low- and adequate-zinc groups, but was 18-fold higher in the high-zinc group than in the other two groups. Liver zinc content varied in relation to dietary zinc level. Biliary excretion of all metals studied was significantly lower in the high-zinc group than in the low-zinc group. The cumulative excretion of zinc, cadmium and mercury over 2.5 h in rats fed these two diets was 6.2 +/- 1.4 vs. 33.5 +/- 7.7, 0.006 +/- 0.02 vs. 22.8 +/- 8.4 and 1.6 +/- 0.6 vs. 14.9 +/- 5.3 micrograms/kg body weight, respectively. A relationship was found between the disposition of metal in liver and the extent of biliary metal excretion. Biliary metal excretion was highly correlated with liver cytosolic non-MT-bound metal; r = 0.999, 0.998 and 0.993 for endogenous + exogenous zinc, cadmium and mercury, respectively.     

Relations between liver cadmium, cumulative exposure, and renal function in cadmium alloy workers

Detailed biochemical investigations of renal function were made on 75 male workers exposed to cadmium and an equal number of referents matched for age, sex, and employment status. The exposed group consisted of current and retired workers who had been employed in the manufacture of copper-cadmium alloy at a single factory in the United Kingdom for periods of up to 39 years and for whom cumulative cadmium exposure indices could be calculated. In vivo measurements of liver and kidney cadmium burden were made on exposed and referent workers using a transportable neutron activation analysis facility. Significant increases in the urinary excretion of albumin, retinol binding protein, beta 2 microglobulin, N-acetylglucosaminidase (NAG), alkaline phosphatase, gamma-glutamyl transferase and significant decreases in the renal reabsorption of calcium, urate, and phosphate were found in the exposed group compared with the referent group. Measures of glomerular filtration rate (GFR) (creatinine clearance, serum creatinine, and beta 2 microglobulin) indicated a reduction in GFR in the exposed population. Many of these tubular and glomerular function indicators were significantly correlated with both cumulative exposure index and liver cadmium burden. Using cumulative exposure index and liver cadmium as estimates of dose, a two phase linear regression model was applied to identify an inflection point signifying a threshold level above which changes in renal function occur. Many biochemical variables fitted this model; urinary total protein, retinol binding protein, albumin, and beta 2 microglobulin gave similar inflection points at cumulative exposure levels of about 1100 y.micrograms/m3 whereas changes in the tubular reabsorption of urate and phosphate occurred at higher cumulative exposure indices. Measures of GFR, although fitting the threshold model did not give well defined inflection points. Fewer variables fitted the two phase model using liver cadmium; those that did gave threshold levels in the range 20.3-55.1 ppm. When cadmium workers with cumulative exposure indices of less than 1100 y.micrograms/m3 were compared with their respective referents only serum beta 2 microglobulin and urinary NAG were significantly increased in the exposed group and these differences were not related to the degree of cadmium exposure.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cadmium levels in the lung,liver, kidney cortex,and urine samples from Australians without occupational exposure to metals

The authors undertook this study to assess levels of cadmium exposure in the general population. Samples of lung, liver, and kidney were obtained from 61 cadavers (43 males, 18 females; 2-89 yr of age, mean age = 38.5 yr) who died from accidental causes and who were subject to postmortem examinations at the John Tonge Centre for Forensic Sciences, Queensland Health Scientific Services, Brisbane, Australia, in 1997 and 1998. Samples of bladder urine were also obtained from 22 cadavers. Tissue and urine samples were analyzed for cadmium, zinc, and copper with inductively coupled plasm (ICP) mass spectrometry. The overall mean values for cadmium in the lung, liver, and kidney cortex samples were 0.13, 0.95, and 15.45 microg/gm wet tissue weight. The average renal cadmium level in subjects with high lung-cadmium levels (n = 13) was 6 microg/gm wet tissue weight higher than that of similarly aged subjects who had medium lung-cadmium levels (n = 30). In females, the average level of cadmium in the liver was 74% greater than in males, and the average liver cadmium in females with high lung-cadmium levels was 100% higher than in males in the same age range who had the same high lung-cadmium levels. Renal cadmium accumulation tended to be greater in females than in males who were in the same age range and who had similar lung-cadmium levels, a result that suggested that there was a higher absorption rate of cadmium in females. The mean value for a urinary cadmium excretion of 2.30 microg/gm creatinine was found in a subset of samples that had a mean age of 39 yr and a renal cortex cadmium concentration of 18.6 microg/gm wet tissue weight. Urinary cadmium excretion rates were correlated more strongly with lung and kidney cadmium content than with age or liver cadmium levels. The results suggest that urinary cadmium excretion may be increased in smokers and could provide some estimate of body cadmium burdens in future Australian epidemiological studies.     

Acute inhalation study in the rat of comparative uptake, distribution and excretion for different cadmium containing materials

Single 2-hr inhalation exposures were conducted at levels of approximately 100 mg/m3 (based on cadmium content) with the use of two cadmium pigments (cadmium red and cadmium yellow), a dust of cadmium carbonate, and a cadmium fume. An air exposed control group also was included. The rate of elimination of cadmium in the urine and feces, and the cadmium levels in selected tissues were measured at several intervals following the exposure. In addition, observations of the animals for clinical signs of toxicity and mortality and measurements of organ weights and body weight were performed. There was no mortality in the control, cadmium red or cadmium yellow exposed groups. In the cadmium carbonate exposed group, 3 out of 52 rats died, and in the cadmium fume exposed group, 25 out of 52 rats died. Cadmium blood levels indicated that cadmium from the cadmium carbonate and fume was absorbed to a greater degree than cadmium from the red and yellow pigments. The major route of elimination of cadmium following exposure to the two pigments was via the feces, with 80% being cleared within 24 hr. Elimination was slower following exposure to the carbonate. The levels of cadmium in the liver and kidneys were much higher following exposure to the carbonate than following exposure to the red and yellow pigments. It appeared that these cadmium compounds were not equivalent with respect to toxicity, absorption, distribution or excretion. Exposure to the two insoluble compounds, cadmium red and cadmium yellow, did not produce mortality and resulted in rapid elimination in the feces with lower tissue levels of cadmium than observed following exposure to the cadmium carbonate.     

Cadmium Levels in the Lung,Liver, Kidney Cortex,and Urine Samples from Australians without Occupational Exposure to Metals

The authors undertook this study to assess levels of cadmium exposure in the general population. Samples of lung, liver, and kidney were obtained from 61 cadavers (43 males, 18 females; 2–89 yr of age, mean age = 38.5 yr) who died from accidental causes and who were subject to postmortem examinations at the John Tonge Centre for Forensic Sciences, Queensland Health Scientific Services, Brisbane, Australia, in 1997 and 1998. Samples of bladder urine were also obtained from 22 cadavers. Tissue and urine samples were analyzed for cadmium, zinc, and copper with inductively coupled plasm (ICP) mass spectrometry. The overall mean values for cadmium in the lung, liver, and kidney cortex samples were 0.13, 0.95, and 15.45 μg/gm wet tissue weight. The average renal cadmium level in subjects with high lung-cadmium levels (n = 13) was 6 μg/gm wet tissue weight higher than that of similarly aged subjects who had medium lung-cadmium levels (n = 30). In females, the average level of cadmium in the liver was 74% greater than in males, and the average liver cadmium in females with high lung-cadmium levels was 100% higher than in males in the same age range who had the same high lung-cadmium levels. Renal cadmium accumulation tended to be greater in females than in males who were in the same age range and who had similar lung-cadmium levels, a result that suggested that there was a higher absorption rate of cadmium in females. The mean value for a urinary cadmium excretion of 2.30 μg/gm creatinine was found in a subset of samples that had a mean age of 39 yr and a renal cortex cadmium concentration of 18.6 μg/gm wet tissue weight. Urinary cadmium excretion rates were correlated more strongly with lung and kidney cadmium content than with age or liver cadmium levels. The results suggest that urinary cadmium excretion may be increased in smokers and could provide some estimate of body cadmium burdens in future Australian epidemiological studies.     

Effects of cadmium on the metabolism of p,p'-ddt [2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane] in rats

The effects of cadmium on the excretion and metabolism of DDT in rats were investigated. The excretion of DDT after a single parenteral administration was modified by the addition of a small amount of cadmium. The time pattern of DDT retention in the whole body was explained by a three-compartment model. An increased level of lipid content in the liver induced by cadmium was accompanied by a relative increase of DDT residue in the liver. This indicates that the effect of cadmium on the metabolism of DDT is mainly due to the change of lipid content in the liver. Since the effect of the cadmium was long-lasting, a significant elevation in the metabolic rate of DDT and a low level of DDT concentration in adipose tissue was observed after the dose of cadmium.     

Effect of acute administration of cadmium on the disposition of copper,zinc, and iron in the rat

Acute administration of subcutaneous doses of cadmium (0.1–1.5 mg/kg) to male rats resulted in high plasma concentrations of copper 24 hr after treatment. In contrast, plasma zinc and iron levels were markedly reduced. The magnitude and significance of the changes in plasma metal ion concentrations were dependent upon the dose of cadmium administered. Liver copper levels were slightly but not significantly increased, but circulating ceruloplasmin levels increased as the total plasma copper increased. Biliary excretion of copper was markedly inhibited after cadmium administration (subcutaneous and oral) and the degree of inhibition was directly related to the dose. Simultaneous parenteral administration of zinc did not counteract this effect. These results suggest that cadmium blocks the excretion of copper into the bile leading to an accumulation of copper in the liver, which in turn, stimulates the synthesis of ceruloplasmin. The mechanisms by which cadmium may inhibit biliary copper excretion are discussed.     

Copper, zinc, and cadmium concentrations in Peromyscus maniculatus sampled near an abandoned copper mine

Concentrations of zinc, copper, and cadmium were determined in soil and liver, kidney, bone and stomach contents of deer mice (Peromyscus maniculatus) from two sites near an abandoned mine and one control site, on Vancouver Island, British Columbia, Canada. Soil concentrations of copper were significantly elevated at the mine and off site vs the reference site. In contrast, there was no difference in soil cadmium and zinc concentrations between the mine and reference site. Concentrations of copper, cadmium and zinc in livers of mice from the mine site were significantly elevated relative to the reference and off site locations. Cadmium kidney concentrations tended to be greater in mice from the mine versus the off site and reference site. No differences in bone cadmium, copper and zinc and, kidney copper and zinc concentrations were noted among mice from the three locations. Diet of mice from mine and off sites contained significantly greater copper concentrations than the reference population; no differences in cadmium or zinc diet concentrations in mice from the three sites were noted. Comparison of ratios of metal concentrations in diet:soil and concentrations in liver:soil suggest that for zinc and copper, soil and diet are of equal importance as a source of metal contamination to these mice. In contrast, cadmium diet:soil and cadmium liver:soil ratios were much greater than one indicative of bioconcentration of cadmium from soil to diet and from soil to liver. For assessing routes of metal exposure, in this case for deer mice inhabiting an abandoned mine site, for copper and zinc, soil will most likely be indicative of exposure conditions. In contrast, concentrations of cadmium in diet will be more representative of amounts that the animal is potentially ingesting. Of further importance is that relative to reference sites, mice inhabiting an abandoned copper mine site have significantly elevated tissue levels of copper. This is turn will provide a route of metal exposure to canivorous birds such as owls and hawks. The toxicological significance of this exposure to birds of prey has yet to be assessed adequately.     

Cadmium concentrations in human liver, blood, and bile: comparison with a metabolic model.

Cadmium concentrations in liver biopsies, blood, and bile were measured by atomic absorption spectrophotometry in 23 patients in connection with routine gallstone operations. On a group basis cadmium in blood was a good indicator of cadmium in liver, and the estimated linear relationship agreed well with calculations from a formerly proposed metabolic model. Cadmium in bile was also analyzed, and an average of about 2.5 ng of Cd/g wet weight was found. This is about 10 times more than would have been expected form the metabolic model and suggests that bile might be an important excretion route for cadmium. Definite conclusions cannot be drawn, however, since the results could not be cross-checked with neutron activation analysis, due to insufficient sensitivity of the latter method.     

Fate and comparative toxicity of metallothioneins with differing Cd/Zn ratios in rat kidney

Metallothioneins with differing Cd/Zn ratios were preparedin vitro from rat liver zinc-thionein by replacing zinc with cadmium and were injected intraperitoneally to female rats. The distribution of cadmium, zinc, and copper in the kidney supernatant fraction was determined using a Sephadex G-75 column. The distribution pattern of cadmium and zinc changed dramatically within 24 hr after the injection. The changes were explained by the degradation and re-synthesis of metallothionein in the kidneys. The necrotic changes of renal tubular lining cells were correlated to the amount of cadmium in the metallothionein but not to the amount of metallothionein (protein).     

Levels of As, Cd, Pb, Cu, Se and Zn in bovine kidneys and livers in Jamaica

Paired liver and kidney samples from 100 free-range cattle in different parts of Jamaica were analyzed for essential and non-essential trace elements. We found significant enrichment of elements in the kidney (K) compared to the liver (L) with the K/L concentration ratios being 5.2 for Cd, 4.1 for Pb, 3.5 for Se and 2.1 for As, but the Cu contents of the kidney were significantly higher with the K/L ratio of 0.45. A large number of kidney and liver samples showed Cu concentrations in the ranges that were associated with deficiency effects in mammals. About 15% of the hepatic samples had Zn concentrations below 20 microg/g, suggesting that there might be zinc insufficiency in some of the animals. Positive associations were found between the metals in both the kidney and liver. On average, the intake of Cd from consumption of both bovine kidney and liver from the island was estimated to be 5.2 microg/day, equivalent to about 7% of the provisional tolerable daily intake (PTDI), although anyone who habitually consumed the few kidneys or livers with >40 microg/g cadmium may be at some risk of exceeding the PTDI. The consumption of offal from local animals did not appear to be an important dietary source of any of the essential microelements.     

Fertility of male workers exposed to cadmium, lead, or manganese.

The effect of exposure to cadmium, lead, or manganese on male reproductive function was examined in 1988-1989 in Belgian blue-collar workers. The workers were exposed to cadmium in two smelters (n = 83; geometric mean urinary cadmium level = 6.94 micrograms/g of creatinine; mean duration of exposure = 24 years), to lead in a battery factory (n = 74; mean blood lead level = 46.3 micrograms/dl; mean duration of exposure = 10.7 years), or to manganese (manganese dioxide) in a dry alkaline battery plant (n = 70; median atmospheric concentration of total manganese dust = 0.71 mg/m3; mean duration of exposure = 6.2 years). Fertility in these workers and in an unexposed population (n = 138) was assessed by examining the birth experiences of their wives through a logistic regression model. The probability of a live birth was not different between the unexposed workers and the cadmium- or manganese-exposed workers before or after the onset of exposure. While the fertility of the lead-exposed workers was somewhat greater than that of the unexposed before the onset of exposure, a significant decrease in fertility was observed during the period of exposure to the metal (odds ratio = 0.65, 95% confidence interval 0.43-0.98).     

Urinary excretion of cadmium, copper and zinc in workers exposed to cadmium

Changes in urinary cadmium, copper and zinc excretion in workers who had considerable exposure to cadmium oxide fumes were investigated over a 5-year period following the cessation of exposure. The 22 male subjects aged 22 to 55 had been welders on automobile parts for periods ranging from 7 months to 23 years, using silver solder which contained cadmium. They were divided into three groups according to levels of urinary cadmium in the first medical examination in 1975: 5 in the high excretion group, 11 in the moderate group, and 6 in the low group. Renal tubular dysfunctions were indicated in most workers in the high excretion group but not in the other two groups. The high and moderate groups showed a rapid decrease in the levels of urinary-excreted cadmium, with biological half-times of 1.42 and 1.21 years, respectively. Excreted cadmium levelled off in the two groups about 1.7 and 1.5 years after the last exposure. Urinary copper excretion in the high cadmium excretion group was about twice that in the moderate and low groups, the difference being statistically significant in comparison with the controls. Urinary zinc excretion was high in all subjects immediately after cessation of exposure but decreased rapidly. After three years it was found that the reduction of urinary zinc was greatest in the high cadmium group. Urinary cadmium showed significant correlations with both copper and zinc. Urinary copper showed a negative correlation with zinc excretion in the high cadmium excretion group and a significant positive correlation in the other two groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dietary assimilation and elimination of Cd, Se, and Zn by Daphnia magna at different metal concentrations

This study examines the influences of Cd, Se, and Zn concentrations in ambient water on the assimilation, elimination, and release budget of metals, and the clearance rate of Daphnia magna through ingestion of phytoplankton diets. With increasing ambient metal concentration over two to three orders of magnitude, the assimilation efficiencies (AEs) of Cd and Se from two green algal species, Scenedesmus obliquus and Chlamydomonas reinhardtii, decreased significantly. In contrast, the Zn AE from ingested food, which typically was low (<7%), was not impacted by the difference in Zn or Cd concentrations in ingested cells. The Cd AE also was reduced significantly by a high Zn concentration in ingested algae, perhaps due to the competitive assimilation between the two metals. Metal elimination was determined after the daphnids were exposed to the radiolabeled diets for 3 d. The elimination rate constant was not dependent on the metal concentration in ingested food. Similarly, the routes of metal elimination (excretion, egestion, molting, and neonate production) were less influenced by the metal concentration. The rapid elimination of Se and Zn may be attributed to the transfer of these metals from mother to offspring. Except at the highest Cd (917 nM) and Se (1,333 nM) concentrations, there was no significant effect of metal concentration on the clearance rate of the animals. Consequently, the metal assimilation in D. magna may play an important role in the regulation of Cd and Se influx into the animals, whereas the regulation of the metal tissue burden in the animals is unlikely to be achieved through the metal elimination. The trophic transfer factors (TTF) of Cd and Se were related inversely to the metal concentration in the water, whereas the TTF of Zn was less variable at different Zn concentrations. The change of TTF with metal concentration will have important implication for ecotoxicity testing using D. magna, especially when the dietary exposure is incorporated.     

Adaptation to soil pollution by cadmium excretion in natural populations of Orchesella cincta (L.) (Collembola)

Population differentiation in Orchesella cincta (L.) (Collembola) populations, from various heavy metal contaminated sites, was studied by comparing cadmium excretion efficiency in first generation (F₁) laboratory individuals. Animals from sites with high metal concentrations in the litter and with a long history of contamination showed significantly higher excretion efficiencies than animals from low pollution, or reference sites. Differences found in the F₁ laboratory animals suggest evidence for genetic differences between the populations.Beneficial and detrimental effects of cadmium excretion were studied in relation to body growth and cadmium concentrations. In chronically exposed animals from an unpolluted site, no physiological acclimation was observed. Excretion efficiency was negatively correlated with body concentrations of cadmium. No detrimental effects were found.Whole-body equilibrium concentrations of cadmium and lead were similar in F₁ animals from the reference site and polluted sites. Significant differences in excretion efficiencies imply that the distribution of toxic metals over body compartments differs, tolerant populations having a higher proportion deposited in the gut. Body concentrations of zinc were consistently higher in animals from the polluted site, during both cadmium and zinc exposure. No detrimental effects of increased cadmium excretion on body concentrations of zinc were observed. Population comparisons of cadmium excretion efficiency data and growth reduction in F₁ laboratory animals showed that both parameters were inversely related. Cadmium and lead contamination were not the sole factors determining tolerance differentiation.