The effect of cadmium ion on the growth,photosynthesis, and nitrogenase activity of Anabaenainaequalis

The growth of $\text{Anabaena}$$\text{inaequalis}$ was significantly inhibited by Cd²⁺ concentrations greater than 0.02 ppm (μg/ml) and completely inhibited at 0.06 ppm (Day 12). Cadmium had no significant effect upon the lag phase of growth or the culture doubling time, but caused the retardation phase to arrive sooner. One ppm Cd²⁺ significantly inhibited the rates of both photosynthesis and acetylene reduction, by $\text{A}$. $\text{inaequalis}$, with complete inhibition at 4 and 20 ppm respectively. Cell sensitivity increased directly with exposure time. Cadmium caused some cell lysis of $\text{A}$. $\text{inaequalis}$ and induced an increase in filament length, heterocyst frequency, and a loss of cellular contents from filament apical cells. The cellular abnormalities observed and the fact that toxicity increased with longer exposure times, suggested that metal toxicity resulted from effects of Cd²⁺ taken up by cells rather than Cd²⁺ at the cell surface.     

The use of XAD-resins for the detection of mutagenic activity in water: I. Studies with surface water

A study of the effects of different XAD-resins, bed volume, flow rate, pH and type of eluent on the extraction of organic mutagens from surface water is presented. XAD-4/8 is as effective as XAD-2 in concentrating organic mutagens from surface water and dimethylsulfoxide (DMSO) is as efficient as acetone in eluting the adsorbed organic mutagens. The latter allows direct testing up to 0.5 ml of DMSO concentrate in the Ames test. Variation of the pH of the water after passing the XAD-4/8, followed by readsorption, shows that the majority of the mutagenic activity due to dissolved organics is adsorbed at neutral pH. Only a minor fraction is readsorbed at pH 3. Further a XAD-4/8 concentrate and a similar concentrate prepared by freeze drying gives similar mutagenic activity. This indicates that many of the organic mutagens are recovered in the XAD-4/8 concentrate.It is concluded that adsorption on XAD-4/8, followed by direct testing of the DMSO eluates in the Ames test, presents a rapid and relatively simple way to detect low concentrations of organic mutagens in surface water. The general suitability of the method is shown for different types of surface water.     

The fate of endosulfan in aquatic ecosystems

Endosulfan, one of the major pesticides used in cotton-growing, is of environmental concern because of its toxicity to fish and its apparent persistence in the environment. This study examines the distribution and degradation pathways for endosulfan in an aquatic system and the processes by which it is removed. In the alkaline waters of the cotton region, hydrolysis is the dominant degradation process. By this mechanism alone, the expected half-lives for the alpha- and beta-endosulfan isomers were found to be 3.6 days and 1.7 days, respectively. Partitioning studies showed, however, that the major proportion of endosulfan would associate with the sediments (log Koc(alpha) 3.6 and log Koc(beta) 4.3). Field studies confirmed the presence of high concentrations in sediments. Microcosm experiments showed that loss of endosulfan was slower than predicted from hydrolysis rates. Models are presented to explain how desorption from sediment limits the loss of endosulfan from a system.