Bound residues: environmental solution or future problem?

The paper examines the issue of bound residues from the viewpoint of the risk assessment procedures employed for environmental protection. It considers, on one hand, the evidence that such residues are so tightly bound to soil organic matter as to be essentially unavailable; and on the other, the perspective that we should not be loading up the environment with compounds whose future behaviour and release we cannot predict. Existing knowledge of the mechanisms by which residues bind to soil organic matter suggests that release will be closely dependent on soil organic matter breakdown. Simple models of organic matter turnover suggest that the release following single applications of individual compounds will be very slow; but the significance of releases following repeated application over many years of a number of compounds needs to be investigated further. Applying environmental risk assessment techniques is complicated by the difficulty in identifying parent molecules and potential metabolites in the bound residue fraction. The paper concludes that for single additions of individual compounds, bound residues probably do represent an environmental solution. But the long-term significance of bound residues formed from multiple additions of a number of compounds is less clear. The paper recommends that future work should emphasise the biological significance of such residues and their release.

Metabolic activity of pathogenic bacteria during semicontinuous anaerobic digestion

In natural environments such as anaerobic digesters, bacteria are frequently subjected to the stress of nutrient fluxes because of the continual changes in the flow of nutrients, and to survive, they must be capable of adapting readily to nutrient changes. In this study, the metabolic activities of Escherichia coli, Salmonella typhimurium, Yersinia enterocolitica, Listeria monocytogenes, and Campylobacter jejuni were studied within culture bags (Versapor -200 filters, 0.22 - microns pore size) in laboratory anaerobic digesters. The metabolic activity of these bacteria was indicated by their adenylate energy charge (EC) ratios and their ability to incorporate [3H] thymidine, which was related to the respective changes in viable number within the culture bags during anaerobic digestion. Fluctuations in the adenylate EC ratios, the uptake of [3H] thymidine, and the viable numbers of E. coli, S. typhimurium, Y enterocolitica, and L. monocytogenes cells were probably due to constant changes in the amount of available nutrients within the anaerobic digesters. The viability of S.typhimurium increased quickly after a fresh supply of nutrients was added to the system as indicated by the uptake of [3H] thymidine and an increase in the adenylate EC ratios. The viable numbers of E. coli, S. typhimurium, Y. enterocolitica, and L. monocytogenes organisms declined rapidly from 10 (7) to 10 (8) CFU/ml to 10(3) to 10 (4) CFU/ml and remained at this level for an indefinite period. The decimal reduction time calculated during the period of exponential decline ranged from 0.8 to 1.2 days for these bacteria. C. jejuni had the greatest mean decimal reduction time value (3 - 6 days).(AU)