F.L. Petrilli

Metabolic deactivation of hexavalent chromium mutagenicity.

Abstract Hexavalent chromium compounds (sodium dichromate, potassium chromate, chromic acid, basic zinc chromate and basic lead chromate) were found to be mutagenic for his − strains of S. typhimurium by inducing both frameshifts and base-pair substitutions. However, addition of either microsomal fractions from rat liver or of human erythrocyte lysates resulted in a complete loss of mutagenicity. As confirmed by chemical analysis, reversal of mutagenicity could be ascribed to reduction of the metal to the inactive trivalent form through a simple oxido-reductive reaction. In fact, reducing agents (ascorbic acid and sodium sulfite) and metabolites (GSH, DPNH and TPNH, either directly tested or obtained by mixing G6PD with S-9 mix) prevented hexavalent chromium mutagenicity, whereas an oxidizing agent (potassium permanganate) totally inhibited reversal of mutagenicity by liver and erythrocyte preparations. Enzymic conversion appeared to be involved in deactivation processes through a large production of TPNH via the hexose monophosphate oxidative pathway and other ancillary systems. On the other hand, microsomal preparations from rat lung displayed an extremely poor inactivating effect on chromium mutagenicity, and those from rat muscle, as well as human serum or plasma, were ineffective. These findings could bear relevance for the elective localization of chromium-induced tumors in human lung and could account for the results of animal carcinogenicity tests, which generally showed the development of tumors, but only at implant sites.

Oxidation of inactive trivalent chromium to the mutagenic hexavalent form

Soluble trivalent chromium compounds (chromium potassium sulfate, chromium nitrate, chromium chloride, neochromium and chromium alum) were inactive for Salmonella typhimurium TA100, even at milligram amounts per plate. No effect could be detected either in the absence or in the presence of rat-liver, lung or muscle microsomal fractions, of rat-muscle mitochondria (with or without ATP), of oxidized glutathione (GSSG), or of human serum, plasma or erythrocyte lysates. Conversely, addition of a strongly oxidizing agent (potassium permanganate) resulted in toxic effects in plates incorporating more than 40--80 microgram of compounds and elicited a dose-effect mutagenic response at 10--40 microgram per plate. These effects could be ascribed to oxidation of chromium from the trivalent to the active hexavalent state. Insoluble chromite, as tested in the spot test, was spontaneously mutagenic, owing to contamination of the industrial product with hexavalent chromium. The results obtained may be useful to interpret the findings of carcinogenicity tests and to predict health hazards linked to chromium.

Metabolic reduction of chromium by alveolar macrophages and its relationships to cigarette smoke.

Pulmonary alveolar macrophages (PAM), obtained by bronchoalveolar lavage from 47 individuals, reduced hexavalent chromium [Cr(VI)] and decreased its mutagenicity. Their specific activity--mostly mediated by cytosolic, enzyme-catalyzed mechanisms--was significantly higher than in corresponding preparations of mixed-cell populations from human peripheral lung parenchyma or bronchial tree, or from rat lung or liver. At equivalent number of PAM, Cr(VI) reduction, total protein, and some oxidoreductase activities were significantly increased in smokers. No appreciable variation could be detected between lung cancer and noncancer patients. In rats, the Cr(VI)-reducing activity of PAM preparations was induced by Aroclor 1254. Thus, alveolar macrophages provide crucial defense mechanisms not only by phagocytizing metals, but also by metabolically reducing Cr(VI). The epithelial-lining fluid (ELF) also displayed some Cr(VI) reduction. Together with already investigated metabolic processes occurring inside lung cells, these mechanisms are expected to determine thresholds in the pulmonary carcinogenicity of chromium.

Metabolic reduction of chromium as a threshold mechanism limiting its in vivo activity.

Various mechanisms tend to reduce hexavalent chromium (Cr(VI] in the organism, both outside and inside target cells. A reducing activity has been demonstrated in the blood (mainly in erythrocytes), in secretions of the alimentary tract (saliva, gastric juice) and in the lumen of terminal airways (epithelial-lining fluid and alveolar macrophages). Preparations of several types of cells from various animal species--including human liver, lung parenchyma and bronchial tree cells--are capable of metabolically reducing Cr(VI) to a variable extent. This process can be ascribed to different cytoplasmic components, e.g. to mitochondria, microsomal fractions and especially to cytosolic fractions, where reduction is partly due to electron donors (e.g. glutathione) and mainly to NADPH-dependent enzyme activities, such as DT-diaphorase. Reduction is not only selectively stimulated by enzyme inducers but also, in rat lung cells, by the repeated intra-tracheal administration of Cr(VI) itself. All these reducing reactions are interpreted as detoxifying mechanisms, which constitute a threshold phenomenon in chromium carcinogenesis.

Survey of the pollution in a coastal area of the Tyrrhenian Sea. aerial photography, physico-chemical and microbiological investigations and mutagenic monitoring

Abstract Investigations were carried out in a coastal area of the Tyrrhenian Sea, which receives wastes from a chemical manufacturing industry. Industrial wastes are combined with domestic sewage prior to discharge into the sea. Warm and alkaline wastewaters carry large amounts of whitish suspended solids, mainly composed of calcium carbonate, calcium sulphate and magnesium hydroxide, which are responsible for an evident visual pollution of the sandy shore and of the facing sea-water body. Alterations of physical parameters (temperature and pH values) were found to affect the investigated coastal area only to a limited extent. Conversely, aerial photographic investigations afforded a more complete picture of pollution spreading. Infrared and chiefly water-penetration images provided information on the underwater environment, and the resulting findings could be correlated with the particle size analysis of sediment samples. Faecal streptococci represented a considerable proportion of total heterotrophic bacteria in waste and sea-water, whereas concentration of total and faecal coliforms was relatively low. These figures suggested a possible selective inactivation of bacteria in industrial waters, which was supported by the findings of survival tests with three bacterial species ( E. coli, Strep. faecalis and S. typhi ). Survival of a virus (type 1 poliovirus) and of a virus antigen (hepatitis B surface antigen or HBsAg) was also investigated under various conditions. Clearance of industrial solids around some bacterial colonies growing in agar plates could be ascribed to aspecific acidification of the medium by bacterial metabolism. Finally, unconcentrated samples of the industrial wastewater failed to elicit any toxic or mutagenic effects for his − strains of S. typhimurium , both in the presence and absence of rat liver microsomal preparations.

MICROBIOLOGICAL EVALUATION OF COASTAL WATERS QUALITY IN THE TYRRHENIAN SEA

ABSTRACT This paper reports the results of a 4-year investigation, concerning the microbiological quality of coastal waters in the Tyrrhenian Sea, for a total coastline length of approximately 180 km. The monitored areas include the Tuscany littoral in the district of Livorno (Leghorn, Italy), three isles (Elba, Capraia and Gorgona) and the terminal tract of two rivers (Calambrone and Cecina). The results obtained were considered for the assessment of the bacteriological and virological pollution of the monitored areas, as well as for the study of the correlation between the different bacteriological parameters (total coliforms, E. coli and fecal streptococci) and between E. coli and animal viruses.