Cadmium accumulation in crops

Cadmium is a heavy metal present in soils from natural and anthropogenic sources. Plant uptake of Cd at levels present in the soil solution is dependent on a system that is largely metabolically mediated and competitive with the uptake system for Zn and possibly other metals. Much of the Cd taken up by plants is retained in the root, but a portion is translocated to the aerial portions of the plant and into the seed. The amount of Cd accumulated and translocated in plants varies with species and with cultivars within species. Soil, environmental and management factors impact on the amount of Cd accumulated in plants. Potential methods of reducing the accumulation of Cd in crops include reduction of Cd input to the soil system, site selection, management practices which decrease the concentration of Cd in the soil solution and its uptake and translocation by plants, and development and production of plant cultivars with the genetic tendency for low Cd uptake. Key words: Cadmium, fertilizers, genetics, uptake, tillage, rotation

A cadmium-tolerant strain of Neocosmospora vasinfecta shows reduced cadmium influx

Neocosmospora vasinfecta was grown in a defined liquid medium and its growth responses to CdSO4 were measured. The specific growth rate of mycelium not previously exposed to cadmium was reduced to 50% by 51 μM cadmium. The growth response to concentrations of cadmium above 50 μM was complex, showing declining and then recovery phases. Inoculum taken from a culture grown to the recovery phase in presence of 100 μM cadmium was cadmium tolerant; a cadmium level of 420 μM was required to reduce its specific growth rate by 50%. Tolerance was not lost by growth in the absence of cadmium. The tolerant mycelium showed markedly reduced net uptake of cadmium as compared with the normal (cadmium sensitive) mycelium. This reduction was due to a decrease in the unidirectional influx of cadmium, with little or no change in efflux. Cadmium toxicity in the normal mycelium was strongly antagonized by calcium but only weakly by manganese or zinc. Calcium also inhibited the uptake of cadmium. Key words: cadmium, calcium, Neocosmospora, tolerance, toxicity, transport.

Relationship of Cadmium-Induced Hypocalcemia with Mortality in Rainbow Trout (Salmo gairdneri) and the Influence of Temperature on Toxicity

Cold-acclimated (6 °C) rainbow trout, exposed to lethal concentrations of cadmium, survived longer than warm-acclimated (12 and 18 °C) trout. Ten-day lethal thresholds indicated that cold-acclimated trout could also resist greater concentrations of cadmium. Calcium concentrations in the plasma of fish, exposed to 0.3 mg Cd/L, declined steadily during the period of exposure when subjected to five thermal regimes, different combinations of acclimation and experimental temperatures. The rate of decline in calcium concentrations was correlated with the rate of mortality. Survival times of 12°-acclimated trout subsequently exposed to cadmium at 6, 12, and 18 °C were inversely dependent on temperature, whereas survival times of trout acclimated to 6, 12, and 18 °C and subsequently exposed to cadmium at acclimation temperatures do not show the same temperature dependence. Survival times of 12 and 18°-acclimated and exposed fish were similar, indicating that temperature compensation may promote longer resistance of 18°-acclimated and exposed fish than when they are acclimated to 12 °C and abruptly transferred and exposed to cadmium at 18 °C. Symptoms of cadmium poisoning of the fish are consistent with the effects of extreme hypocalcemia and are similar to those reported in the literature for various fish. The decline of calcium concentrations in the plasma may be the direct cause of mortality. Key words: Cadmium, temperature, hypocalcemia, rainbow trout, Salmo gairdneri, toxicity

Sorption of Cadmium and its Effect on Growth and the Utilization of Inorganic Carbon and Phosphorus of Two Freshwater Diatoms

Cadmium was rapidly sorbed by Asterionella formosa and Fragilaria crotonensis during the first 5–10 min of exposure (0.05 to ~9 μg Cd∙L−1), followed by a hyperbolic increase in the cellular cadmium content as a function of time. Results obtained from experiments conducted in the light and dark, experiments using live and dead populations, and cellular site location studies imply that the sorption of cadmium by A. formosa is partially an active process, but for F. crotonensis it appears to be passive. Populations of A. formosa exhibited a corresponding decrease in the growth rate as the ambient cadmium concentration was increased from ~2 to ~9 μg∙L−1. In contrast, the growth rate of F. crotonensis was unaffected at levels ranging from ~0.05 to ~9 μg Cd∙L−1. The utilization of inorganic carbon by A. formosa was unaffected at ~4 μg Cd∙L−1, but reduced 45% at ~9 μg Cd∙L−1. The utilization rates of carbon and phosphorus by F. crotonensis were reduced at the lower cadmium concentrations and enhanced at the highest. Key words: cadmium, toxicity, sorption, diatom, Asterionella formosa, Fragilaria crotonensis

Polarographic Studies on the Nature of Cadmium in Scallop, Oyster, and Lobster

Free and bound forms of cadmium were determined in raw shellfish by use of differential pulse polarography and atomic absorption spectrophotometry. Free cadmium is defined by its polarographic peak potential of −0.62 ± 0.02 V (saturated calomel electrode) in solvent washed ammonium sulfate extracts. Bound cadmium was determined by subtracting the free cadmium from the total cadmium present in the meat. Both scallop (various species) and American lobster (Homarus americanus) muscle tissues contain no free cadmium. Oyster (various species), on the other hand, had a considerable percentage (~50%) of its total cadmium present as free cadmium, a phenomena as yet unexplained. The detection limit for free cadmium is approximately 0.05 μg/g raw tissue. Key words: cadmium, polarography; free cadmium, oyster, lobster, scallop

Changes in the Predator–Prey Behavior of Fathead Minnows (Pimephales promelas) and Largemouth Bass (Micropterus salmoides) Caused by Cadmium

Increased prey vulnerability was demonstrated for fathead minnows (Pimephales promelas) undergoing acute (24-h) and subacute (21-d) sublethal cadmium exposure prior to interacting with largemouth bass (Micropterus salmoides). The lowest acute and subacute cadmium concentrations that increased prey vulnerability were 0.375 and 0.025 mg Cd/L, respectively, with the latter well below the maximum acceptable toxicant concentration for fathead minnows. Prey exposed to cadmium displayed altered behavior patterns, including abnormal schooling behavior. Key words: cadmium, behavior, predator–prey, bioassay, Micropterus salmoides, Pimephales promelas

Transfer of Cadmium from Soil to Vegetable Crops

A pot experiment was conducted in order to study the transfer of Cd from soil to the vegetable crops namely Lettuce (Lactuca sativa L.), Spinach (Spinacia oleracea L.), Lal sak (Amaranthus tricolor L.) and Data sak (Amaranthus spinosis L.). The mean transfer factors (concentration in plant dry weight / concentration in soil dry weight) varied from 2.030 to 6.785 in root and 0.166 to 0.525 in shoot. The following mean Cd-transfer factors (DW /DW) were obtained; Lettuce (root: 6.785, shoot: 0.271), Spinach (root: 4.775, shoot: 0.385), Lal sak (root: 2.03, shoot: 0.166) and Data sak (root: 3.445, shoot: 0.525). The transfer factor of Cd in roots of vegetables decreased in the order: Lettuce>Spinach>Data sak>Lal sak; while in shoots it was Data sak>Spinach>Lettuce>Lal sak. Key words: Cadmium, transfer, soil and vegetables crops. Bangladesh J. Sci. Ind. Res. 42(3), 327-334, 2007