The effect of EDTA on cadmium and zinc uptake and toxicity in Lemna trisulca L.

Lemna trisulca was grown in axenic cultures with regular replacement of a filter-sterilized medium. The effect of EDTA on the uptake and toxicity of Cd and Zn was examined using a two-way factorial design of varying Cd or Zn concentrations and available EDTA. When the level of available EDTA was in excess of the Cd or Zn concentration, uptake in Lemna trisulca was reduced by 96 to 99%, and correspondingly, multiplication rates were unaffected by elevated Cd or Zn concentrations. The proportion of EDTA available for chelating Cd and Zn was the amount of EDTA in excess of the Fe concentration. The antagonistic effect of the chelator EDTA suggests that, for L. trisulca, it is the free ion activity and not the total metal concentration which determines Cd and Zn uptake and toxicity.Chelators are an essential component of a complete nutrient medium and should be included when measuring metal toxicity in aquatic plants, since Lemna trisulca grown without EDTA had low multiplication rates and appeared stunted and chlorotic. The chelator : Fe ratio, however, should be defined and controlled to avoid confounding the measurement of metal toxicity with metal-chelator interactions.     

Cadmium kinetics in freshwater clams. III. Effects of zinc on uptake and distribution of cadmium inAnodonta cygnea

Freshwater clams (Anodonta cygnea) were exposed to Cd²⁺ (25 g/L) or to Cd²⁺ (25 g/L) plus Zn²⁺ (2.5 mg/L). In the presence of zinc, uptake of cadmium in whole clam was halved. In organs such as the gills, mantle, and labial palps a still larger reduction of Cd accumulation occurred. By contrast, accumulation in midgut gland and kidney was hardly affected by the presence of zinc. It is shown that in the gills zinc competes with cadmium for metal binding sites both within the particulate fraction and the high-molecular weight fraction of the cytosol. Zinc probably did not induce an enlarged synthesis of specific metal-binding, metallothionein-like, proteins. In conclusion, zinc exerts antagonistic effects on uptake of cadmium by gills, and accelerates Cd transport from the gills towards the internal organs.     

Bioconcentration and depuration of copper, cadmium, and zinc mixtures by the freshwater amphipod Hyalella azteca

The uptake and elimination of copper (Cu), cadmium (Cd), and zinc (Zn) by the amphipod Hyalella azteca during exposure to the metals singly and in various combinations was examined in controlled laboratory experiments. In single metal exposures the accumulation of all metals was rapid and increased with exposure time. Copper elimination was slower compared to that for zinc and for cadmium no elimination was detected after 5 days in clean water. In the two-metal mixtures it appears that the presence of one metal influenced the bioconcentration of the other, since the bioconcentration factor (BCF) for copper was higher in the presence of cadmium than in the presence of zinc and in the case of cadmium, the decrease of K(1) values from cadmium single exposure to the binary and tertiary mixtures suggests possible inhibition of cadmium uptake by the other metals. In the case of the three-metal mixture the situation is less clear, with both increased and decreased BCFs recorded, in comparison to single-metal and two-metal mixtures, suggesting both stimulation and inhibition of metal accumulation.     

Effect of ethanol on cadmium uptake and metabolism of zinc and copper in rats exposed to cadmium

Effects of chronic administration of cadmium and ethanol, alone as well as in combination, on the uptake of cadmium and its interaction with other essential trace elements in various tissues of adult rats were investigated. Cadmium given in combination with ethanol led to a pronounced increase in cadmium absorption and accumulation in all the tissues studied relative to both non-exposed controls and rats treated with cadmium alone. Both cadmium and ethanol exhibited specific effects on copper and zinc levels of the tissues. These effects often were significantly altered when the animals were co-exposed to cadmium and ethanol. The results suggested that although both cadmium and ethanol individually pose a hazard to essential trace metal homeostasis of various organs, co-exposure can pose a major threat since animals exposed to ethanol absorb much more cadmium than their unexposed counterparts.     

Effect of temperature on cadmium and zinc uptake by the midge larvae Chironomus riparius

The effect of temperature (5 to 25°C) was studied on the uptake of cadmium and zinc by larvae of the midge Chironomus riparius, using artificial chemically defined solutions. The influence of prior acclimation of midge larvae at five temperatures on metal uptake was examined. At all acclimation temperatures metal uptake in organisms increased with increasing exposure temperature. Among the different temperature exposure groups the effect of temperature acclimation on metal uptake is rather variable and a general pattern can not be distinguished. The integration of the different temperature effects explains 69% of the total variation in cadmium uptake and 68% of the total variation in zinc uptake by midge larvae. The factor that accounts for respiration explained 59% of the cadmium uptake and 60% of the zinc uptake by midge larvae. The apparent activation energies for larval metal uptake are much higher than the activation energy for the free diffusion of the cadmium or zinc ion but close to the activation energy for respiration, showing that metal uptake by midge larvae is largely controlled by active physiological rather than by passive diffusional processes.     

Cadmium and the food chain: the effect of dietary cadmium on tissue composition in chicks and laying hens.

The cadmium content of body tissues and eggs was studied in broiler chicks and laying hens fed diets supplemented with 3, 12, and 48 microgram/g of cadmium. The 48 microgram/g level was selected as a slightly toxic level while the lower levels were felt to be representative of the amounts of cadmium which would occur in feedstuffs due to environmental contamination. All levels of cadmium resulted in increased cadmium content of kidney while only 12 and 48 microgram/g resulted in increases in the cadmium content of liver and muscle. As little as 3 microgram/g cadmium consistently increased the cadmium content of liver and muscle but this did not prove to be statistically significant. The transfer of dietary cadmium to the egg was found to be very low. Only the 48 microgram/g level resulted in an increase in cadmium content of the egg. This dietary treatment also resulted in reduced egg production and egg shell thickness.     

Influence of essential elements on cadmium uptake and toxicity in a unicellular green alga: the protective effect of trace zinc and cobalt concentrations

Within the biotic ligand model (BLM) construct, major cations are considered to be simple competitors for metal binding to uptake sites and may offer some protection against metal-induced toxicity, but the influence of essential trace elements and cell preconditioning to different micronutrient concentrations on metal uptake and toxicity is considered negligible. To test these underlying assumptions, we monitored Cd uptake and toxicity in a green alga (Chlamydomonas reinhardtii) after long-term exposures (60 h) to a range of environmentally realistic free Zn(2+) , Co(2+) , Fe(3+) , Mn(2+) , Ca(2+) , and Cu(2+) concentrations buffered with nitrilotriacetic acid. A 200-fold increase in free [Mn(2+) ] as well as a 100-fold increase in free [Fe(3+) ] did not affect Cd uptake or toxicity, whereas a 50-fold increase in free [Ca(2+) ] effectively offered some protection, as predicted by the BLM. However, a 10-fold increase in free [Cu(2+) ] significantly enhanced Cd toxicity by a factor of approximately 2, whereas a 100-fold increase in free [Zn(2+) ] and [Co(2+) ] from 10(-11) to 10(-9) M significantly decreased Cd uptake and toxicity by more than twofold. These effects did not change with prior algal acclimation to different essential micronutrient concentrations. Low essential trace metal concentrations may strongly affect the uptake and toxicity of Cd in freshwater algae and should be taken into consideration in future developments of the BLM.     

Cadmium accumulation in rat organs after extended oral administration with low concentrations of cadmium oxide

Rats were exposed to dietary cadmium oxide (CdO) (2.80 and 7.15 ppm Cd) for 60 days. Between days 20 and 36 of the feeding experiment, only 7.15 ppm Cd significantly reduced body weight, while an improved food utilization was recorded at both dietary Cd concentrations between days 36 and 50. After 40 and 60 days of exposure, Cd concentrations of selected organs and tissues and the excreta were recorded by atomic absorption spectroscopy. Compared to the control animals, Cd levels of hair, bone (femur), blood, and testes did not increase. Soft tissues (liver, kidney, lung, and spleen) displayed significantly elevated Cd concentrations after 40 and 60 days in both dosage groups. An increased level of Cd in muscle was observed in one group only (7.15 ppm, day 40). Maximum Cd levels were 11.6 ppm in liver and 9.75 ppm in kidney on a dry weight basis, reflecting a 68- and 50-fold accumulation of the metal compared to the controls. Only absolute weights of lung and liver decreased slightly in the higher dosage group, while relative weights of all organs investigated were not affected by Cd. The ratios in fecal Cd levels between control and CdO-treated animals partly reflected the Cd concentration ratio between the respective diets. No increase in the urinary Cd level was found during the feeding trial. The significance of Cd accumulation in organs, tissues, and excreta and their value as indicators for CdO exposure are discussed.     

Competition among zinc, manganese, and cadmium uptake in the freshwater alga Scenedesmus vacuolatus

In the present study, Zn and Mn competition with Cd uptake was investigated in the freshwater alga Scenedesmus vacuolatus. Scenedesmus vacuolatus was exposed to experimental media with Cd and either Zn or Mn in short-term experiments; long-term experiments were undertaken to investigate the effect of growth on Cd accumulation. Cadmium accumulation in S. vacuolatus could be detected at very low exposure concentrations (free Cd2+, 2 x 10(-14) to 1 x 10(-11) M), and uptake was proportional to the free-Cd2+ concentration. Zinc was an effective competitive inhibitor of Cd uptake when the Zn2+ to Cd2+ ratio was greater than 14 in the exposure medium, whereas Mn competed with Cd for uptake above a Mn2+ to Cd2+ ratio of greater than 10,000. Binding constants for Cd and Zn affinity to the transport sites were determined (KZn and KCd). Values for KZn were slightly higher (log K = 9.4-9.8) than values for KCd (log K = 8.9-9.8). In contrast, Cd seemed not to compete with the Mn-binding sites for uptake over the Mn concentration range from 1 x 10(-10) to 1 x 10(-8) M. Determined values for the binding constants of Zn and Cd show that a simple model can be applied to predict Cd uptake at known Zn and Cd concentrations. The environmental implications of these results are discussed with respect to potential Cd toxicity for aquatic organisms.     

Inhibition of intestinal calcium uptake by cadmium and the effect of a low calcium diet on cadmium retention

The direct effect of cadium (Cd) on the in vitro uptake of calcium by rat duodenum was examined by incubating mucosal tissue for 1 to 5 min in an isotonic medium containing ⁴⁵Ca with [³H] inulin included to correct for calcium (Ca) uptake associated with the space accessible to inulin. Cadium inhibited a second phase, time-dependent uptake of Ca which is influenced by vitamin D status and dietary levels of calcium. Cadium had no effect on either an initial rapid uptake of Ca (this is complete within one min) or the inulin space of the intestinal mucosa. Kinetic analysis of the Cd inhibition using 1.0 and 3.0 mm Ca against 0.0–1.0 mm Cd demonstrated Cd was a noncompetitive inhibitor with a K_i of 0.8 mm. Alternatively, Ca did not inhibit ^115mCd uptake in animals fed a normal diet. Furthermore, in animals fed a diet low in Ca for seven days, Cd uptake was not affected despite an increased Ca uptake.Whole-body retention and distribution studies of ^115mCd demonstrated that young rats pair-fed a low Ca diet for seven days retained more ^115mCd for nine days from a single oral dose of 100 nmol of CdCl₂ than control animals fed a Ca replete diet. The low Ca diet influenced organ distribution causing more Cd to be retained in the small intestine and kidneys. However, there was no significant change in the sum of the total Cd content in the kidney and liver which are the major sequestering organs of absorbed Cd.     

Kinetic uptake of bioavailable cadmium,selenium, and zinc by Daphnia magna

Kinetic uptake of Cd, Se(IV), and Zn by Daphnia magna from the dissolved phase was determined using radiotracer techniques in moderately hard water. The metal influx rate and distribution in the soft tissue and the exoskeleton of the daphnids as influenced by metal concentration, inorganic ligands including pH, Ca2+ and SO4(2-), and body size were quantified. When the metal concentrations were <180 nM for Cd and <769 nM for Zn, the concentration factor in daphnids increased linearly within the 12 h of exposure. At a higher concentration, apparent steady state was reached after 3 h of exposure. Cadmium and Zn distribution in the soft tissues was not affected by the total ambient concentrations, whereas Se distribution in the soft tissue decreased by 7 to 10% with increasing Se concentration from 16 to 643 nM. A linear positive power relationship was found between the influx rates of the metals and the ambient concentrations. The concentration factor for Se, however, decreased significantly with increasing Se concentration in water. The influx rate of metals was inversely related to the body size in a power function. When the pH in ambient water increased from 5.0 to 7.0, the influx rate of Cd, Se, and Zn increased by 2.9, 16.6, and 4.1 times, respectively. The influx rates of Cd, Se, and Zn decreased by 6.9, 8.7, and 4.4 times, respectively, with an increase in Ca2+ concentration from 0.6 to 5.1 mM. In contrast, the uptake rates of all three metals were not significantly affected by the SO4(2-) concentration. The majority of accumulated Se was distributed in the soft tissues after 12 h of exposure, whereas Cd and Zn were about evenly distributed in the soft tissue and exoskeleton. Any changes in pH, Ca2+, and SO4(2-) concentrations did not apparently affect their distributions in the daphnids. Our study provides important kinetic data necessary for delineating the exposure routes and for further development of the biotic ligand model in Daphnia. Using a bioenergetic-based kinetic model, we showed that the dissolved uptake is dominant for Zn accumulation (>50%). For Cd and Se, dietary exposure is dominant when the bioconcentration factors of these metals in phytoplankton are at the high end.