EXPERIMENTAL UPTAKE OF STRONTIUM-85 BY FRESH-WATER ORGANISMS

Transformation of the chemical composition of surface waters in the area of the exploited Lomonosov diamond deposit (NW Russia)

The specific objective of this study was to investigate the changes in the chemical composition of river waters during the exploitation of the Lomonosov diamond deposit and the danger of these changes for the ichthyofauna. It was found that the Ca-HCO₃ composition of river water both upstream and downstream from the quarry was almost identical before discharge of the drainage waters into the river. In subsequent years, the water downstream from the quarry acquired a Na-HCO₃ composition, and then a Na-HCO₃-Cl composition and TDS increased by 2.5 times. With respect to Fe, Mn, and Mo, concentrations that are above the maximum permissible concentrations (MPCs) for fishery rivers are apparent. At the same time, elevated Fe and Mn concentrations are associated with the natural composition of river water. The negative influence of drainage waters is manifested only with respect to the high concentrations of Mo. An important role in increasing Mo concentrations in drainage waters is played by the processes of hydrolysis of sodium aluminosilicates and mixing of fresh water with salt water. The concentrations of Sr, B, Ba, V, and Cr in drainage waters are higher than those in surface waters. However, they generally do not exceed the concentrations of the current MPCs. The source of Cr, Ba, Ni, and V in the drainage waters can be the products of the kimberlite magmatism. The possible impacts of metals effects on fish are presented.

Bioavailability of waterborne strontium to the common carp, Cyprinus carpio, in complexing environments

The uptake of strontium (Sr) and calcium (Ca) in the common carp, Cyprinus carpio, was studied in chemically defined freshwater in the presence of the complexing ligands, ethylenediaminetetraacetic acid (EDTA), and nitrilotriacetic acid (NTA). The uptake rates were measured in the whole body, gills, and blood of the fish after an exposure period of 3 h. The uptake rates were determined by using the radiotracers (85)Sr and (45)Ca, and analyzed as a function of the free-ion activity of Sr and Ca in water. Although Sr(2+) activity decreased, the uptake of Sr showed an increase at relatively low concentrations of EDTA and NTA, and a decrease at relatively high concentrations. This can be explained by the decreased competition between Sr(2+) and Ca(2+) at the gill uptake sites due to approximately 30-140-fold higher affinity of EDTA and NTA for Ca(2+) than Sr(2+). With decreasing Ca(2+) activity, Ca uptake rates decreased in the presence of EDTA and NTA, but the effect of NTA was less pronounced. A Michaelis-Menten type competitive inhibition model was derived that could predict the whole-body Sr and Ca uptake rates, taking into account the ambient Sr(2+) and Ca(2+) activities in the presence of EDTA. In case of NTA, the uptake rates were found to be 1.5-3.2 times higher than what was predicted by the model. When the fish were exposed to complexing environments in the complete absence of Ca, an increased uptake of Sr was still observed in case of NTA, but not EDTA. The increased uptake in the presence of NTA is attributed to the direct uptake of SrNTA(-) and CaNTA(-) complexes from water. The results reveal that the uptake of Sr and Ca in carp is not merely a function of the free metal-ion activity but that certain complex species may contribute significantly to overall uptake.

Effect of temperature on the uptake of waterborne strontium in the common carp, Cyprinus carpio (L.)

The effect of temperature on the uptake kinetics of strontium (Sr) in the common carp (Cyprinus carpio) was studied in vivo, exposing pre-acclimated fish to a wide range of Sr concentrations in water (Sr(total)=0.2-10,000 microM; Ca(total)=348 microM) at 10, 20, 25 and 30 degrees C. Sr uptake rates were determined in the whole body, gills and blood of the fish after an exposure period of 3 h and were analyzed as a function of the free-ion activity of Sr and Ca in water. The uptake of Sr(2+) by the whole body, gills and blood increased with temperature and showed saturation kinetics with the increase of Sr(2+) activity. Analyzing the observed uptake rates with a Michaelis-Menten type model showed that the kinetic parameters (J(max), K(m) and K(i)) for both Sr(2+) and its analogue Ca(2+) are temperature dependent. Thermodynamic analysis of the temperature effects indicates that the Arrhenius activation energies (E(a)) required for Sr(2+) uptake (91.9 kJ mol(-1)) and Ca(2+) uptake (105.9 kJ mol(-1)) in the whole body of carp were constant over the temperature range 10-25 degrees C and showed a break in the Arrhenius plots above this temperature. The Arrhenius plot for the Sr(2+) uptake in blood was similar to that for the whole body uptake with an E(a) of 98.1 kJ mol(-1). However, the E(a) for Sr(2+) uptake in gills was much smaller and constant (58.1 kJ mol(-1)) over the temperature range of 10-30 degrees C. For a temperature change from 10 to 25 degrees C, the Q(10) for Sr(2+) uptake in whole fish, gills and blood were 3.71, 2.29 and 4.05, respectively. Compared with Ca(2+) uptake, Sr(2+) uptake appears to require a lower activation energy for transport across the solution body interface in carp. The similar pattern of Arrhenius plots and magnitude of activation energies for Sr(2+) uptake both in blood and whole fish suggest that the uptake into the blood across the basolateral membrane is the rate-limiting energy barrier and hence dictates the overall uptake rate of Sr(2+) in whole fish.

A mechanistic model for the uptake of waterborne strontium in the common carp (Cyprinus carpio L.)

The release of radioactive strontium to the environment is of concern due to the strong accumulation of this calcium resembling element in the bone and other tissues. To predict the effects of changes in environmental conditions on the uptake of Sr2+ and Ca2+ by freshwater fish, a Michaelis-Menten type model is introduced that accounts for the effects of chemical speciation, hydrogen ion activity, and metal ion competition. The uptake kinetics were characterized in vivo from short-term exposure experiments using the common carp (Cyprinus carpio) as the model organism. Fish were exposed to a wide range of waterborne Sr2+ (0.2-10,000 microM) and Ca2+ (10-10,000 microM) concentrations and water pH (5.0-8.5). Strontium uptake by the whole body of fish increased with increasing Sr2+ activity, displaying saturation kinetics, but decreased significantly with increasing Ca2+ and H+ activities in the water. Likewise, calcium uptake by the fish decreased with increasing Sr2+ and H+ activities in the water. The model fitted to the pooled data explains 97.5% of the variation in Sr2+ uptake and 86% in Ca2+ uptake over the wide range of exposure conditions and reveals that Sr2+ and Ca2+ inhibit each other completely competitively, while H+ inhibits the uptake of both metal ions in a partially noncompetitive way. This model can be used as a mechanistic tool to predict the uptake of these metals in carp under variable conditions.