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The quality control of wastewater treatments was monitored using selected novel and classical physicochemical and microbiological indicators, and the associations of the treatments with the effluents was analyzed. The microbiological indicators monitored were heterotrophic plate count (HPC), total coliforms (TC), fecal coliforms (FC), fecal streptococci (FS), sulfite-reducing clostridia (SRC), Pseudomonas aeruginosa, and Salmonella spp. The stages of wastewater treatment also were evaluated through determination of ammonia; biological oxygen demand (BOD(5)); chemical oxygen demand (COD); chloride; conductivity; suspended dissolved and total solids; fats; nitrate, nitrite, and total nitrogen; pH; phosphate and total phosphorus. Additional indicators included the Escherichia coli growth inhibition (IGEC) bioassay for assessing whole effluent toxicity, spectral determinations between wavelengths (lambda) 190-650 nm, and total (TP) and soluble (SP) protein contents. Of the more common physicochemical parameters, only BOD(5), COD, suspended and total solids, and fats showed a statistically significant reduction between raw water and effluent; for the microbiological indicators, significant reduction was seen only for HPC, FC, and Ps. aeruginosa. We suggest that determinations of Ps. aeruginosa be commonly used as an indicator of wastewater quality. Spectral analysis--most notably the values of absorbance at 225, 255, and 295 nm-revealed a statistically significant correlation with several physicochemical parameters. Statistical analysis of SP and TP values showed them to be good indicators of contamination. The quantitative study of Salmonella spp. and the results of the IGEC bioassay show the need for close control of infectious and toxic risks in wastewater and effluents.

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Dithiocarbamates (DTCs) are chemicals featuring a great chelating capacity. The toxicological study of DTCs is very important in view of their relatively simple synthesis and wide array of sanitary and industrial applications. In this study, the toxicity of some of the more recently synthesized DTCs is determined using an extremely simple bioassay, described in previous studies, based on the inhibition of growth of Escherichia coli (IGEC). The lowest-observed-effect concentration (LOEC), the median effective concentration (EC(50)) and no-observed-effect concentration (NOEC) of the following sodium dithiocarbamates was determined: N-benzyl-N-methyldithiocarbamate x 2H(2)O, N-benzyl-N-isopropyldithiocarbamate x 3H(2)O, N-benzyl-N-ethyldithiocarbamate x 2H(2)O, N-butyl-N-methyldithiocarbamate x 2H(2)O, N,N-dibenzyldithiocarbamate x 2H(2)O and N-benzyl-2-phenethyldithiocarbamate x 4H(2)O. Our results showed N,N-dibenzyl-DTC to be the least toxic of the tested substances, with an EC(50) value of 1,269.9 micro g ml(-1), whereas N-butyl-N-methyl-DTC and N-benzyl-N-methyl-DTC, with respective EC(50) values of 14.9 micro g ml(-1) and 23.5 micro g ml(-1), were the most toxic. Regression analysis showed, through exponential models, that the degree of toxicity of this group of substances correlated with the molecular weight of the compound, the molecular weight of the smallest chemical radical linked to the dithiocarbamate group and the number of benzene rings present in the molecule. The consideration of these models allows us to establish that in general terms the toxicity of DTCs decreases exponentially with a greater molecular weight and the number of benzene rings.