Long-term monitoring of aldicarb residues in groundwater beneath a Canadian potato field.

Four shallow monitoring wells beneath a potato field to which Temik (active ingredient--aldicarb) had been applied were sampled up to 19 times over six years. These samples were regularly analyzed for aldicarb sulfoxide, aldicarb sulfone and nitrate and less frequently for major ions and for pH, EH, dissolved oxygen and alkalinity. Pesticide residue concentration in groundwater was related both to time after application and to the elevation of the water table, a measure of groundwater recharge. This dependence on recharge indicates storage in the unsaturated zone. The presence of relatively high residues four years after the last application is due to this storage phenomenon and to water and soil conditions, particularly low temperature, that inhibit the hydrolysis of the active species.

In vitro DNA synthesis on smooth membranes observed by fluorescence.

Smooth membranes have been isolated from a human diploid line of lymphocytes. These membranes exhibit an endogenous DNA-synthesizing capability which is partially destroyed by prior treatment with RNase. In order to ascertain the role of the membranes in the DNA synthesis we have examined the conformation of the membrane proteins by observing fluorescence changes of the intrinsic probe, tryptophan. We have observed that on addition of the deoxynucleoside-5'-triphosphates, which permits DNA synthesis, there are fluorescence changes due to the tryptophan residue; when DNA synthesis is prevented by omitting some of the precursor triphosphates, fluorescence changes are absent. These effects have been observed with plasma and nuclear membrane fractions; the former may contain a small fraction of the latter. Similar membrane preparations from non-lymphoid cells do not process the endogenous DNA-synthesizing system, as shown by the lack of incorporation of radioactive precursors of fluorescence changes.