Carryover of cadmium from feed in growing pigs.

Growing male pigs were exposed to cadmium (Cd) at levels around 1 and 10 mg kg(-1) feed for up to 12 weeks, administered as CdCl2 or Cd-cysteine (CdCys). Pigs exposed to 10 mg kg(-1) showed decreased growth during the last 3 weeks. Liver and kidney concentrations of Cd continuously increased over the entire 12-week exposure, exceeding the European Union limits of 1.0 mg kg(-1) (kidney) and 0.5 mg kg(-1) (liver) within 3 weeks at the feed level of 10 mg kg(-1). A switch to clean feed after 3 weeks for 5 or 9 weeks resulted in steadily decreased levels in kidney and liver, which could be completely attributed to organ growth. At the lower feed level, the level in kidney exceeded the limit almost twofold after 12 weeks, but not after 3 weeks. Liver levels remained below the limit. Metallothionein (MT) levels in livers showed a steady decrease in both untreated and treated animals over time. In kidney such a decrease was only observed in control animals, whereas in the highest-dosed animals the MT concentrations steadily increased. The observed carryover of Cd from feed to liver and kidney was modelled by means of a simple transfer model relating levels in feed via MT levels to accumulation of Cd. Using this model, it was shown that the exposure period of growing pigs to feed containing the European Union limit of 0.5 mg kg(-1) feed should be less than 12 weeks in order to prevent Cd levels in the kidneys to exceed the European Union limit.

Toxicity, accumulation, and retention of zinc by carp under normoxic and hypoxic conditions.

Zinc is an essential micronutrient that becomes toxic at elevated concentrations. Under hypoxic events, i.e., temporal depletion of oxygen, the toxicity of Zn increases for fish, apart from the direct effects of the reduced oxygen levels. This enhanced toxicity currently is explained by the increased ventilation rates under hypoxia, causing a higher water flow over the gills. However, the few experimental studies available on the uptake of heavy metals under hypoxia draw contradictory conclusions. The present study verifies the enhanced zinc toxicity under hypoxia and tests whether accumulation of zinc is increased in common carp, Cyprinus carpio (L.). Second, the effect of acclimatization to three oxygen levels (100, 50, and 25% saturation) on the zinc uptake and elimination was studied in a standard radiotracer uptake-and-elimination study for 63 d at 100 nmol/L Zn and 25 degrees C. The sensitivity of carp for Zn was threefold higher under hypoxia than at normoxic conditions. The lethal concentration for 50% of the population after 96 h (96-h LC50) for normoxia and hypoxia (25%) were 149 (91-317) and 55 (30-100) micromol/L Zn, respectively. However, the kinetic data indicate that zinc uptake and elimination are not altered under hypoxia for common carp. Moreover, observed uptake rates are considerably lower than predicted from a ventilation-and-diffusion-regulated uptake mechanism. Setting these results in the framework of similar experiments of other investigators, we conclude that, in general, metal uptake in fish is not related to its ventilation rate within a normal physiological range.

The toxicokinetics of cadmium in carp under normoxic and hypoxic conditions.

Temporal depletion of oxygen, i.e. hypoxic events, frequently occurs in natural waters. It has been suggested that accumulation of micro-pollutants increases in aquatic animals as a result of an increased ventilation rate during such occasions. The observed increased toxicity under hypoxia of micro-pollutants may support this hypothesis, but for heavy metals the available uptake studies are contradictory. The present study tests whether accumulation of cadmium in common carp, Cyprinus carpio (L.) is increased under hypoxia and if the toxicokinetics are altered. A cadmium toxicity study was performed in which the cadmium uptake rates were determined using the radiotracer 109Cd under hypoxia and normoxia. The cadmium toxicokinetics were studied with radiotracer experiments at 100% air saturation, 50%, and 25% saturation from 6.5 nmol/L Cd at 25 degrees C. We could confirm the higher sensitivity of carp to cadmium under hypoxia. Hypoxic conditions did not influence the uptake rates or the accumulation dynamics. Therefore, the increased sensitivity of carp for Cd under hypoxia cannot be explained by a higher Cd body burden, initiated by a higher uptake rate or lower elimination rate under hypoxia. Additional, possible indirect effects, such as internal anoxia due to gill damage, could play a role in Cd toxicity under hypoxia.

Uptake, biotransformation, and elimination of 99Tc in duckweed.

Aquatic plants may play an important role in the environmental fate of the long-lived radioactive waste product 99Tc. Aquatic plants show a strong accumulation and retention of Tc, even after they have died. This study focuses on possible bio-organic Tc compounds formed in the water dwelling plant duckweed to possibly explain the accumulation and retention. Moreover, a change in chemical speciation often implies a different fate and behaviour in the biosphere. A mild separation technique was used to distinguish between reduced Tc species and TcO(4)(-). Accumulation experiments suggested that reduction of Tc(VII)O(4)(-) and subsequent complexation are responsible for the accumulation of Tc in duckweed. A steady state concentration of TcO(4)(-) in duckweed was reached within 24 h, but the total concentration of Tc increased continuously. Only a small part (