Screening of Illicit Toxic Substances Discharged in Chemical Toilet Sludge

Abstract

This article presents an integrative approach, using toxicological and chemical analyses, to screen for toxic substances that could be illegally added to the chemical-toilet sludge received at the wastewater treatment plant of the Montreal urban community. Four toxicity tests (Microtox, bacterial-respiration, root-elongation, and seed-germination tests) were used to establish the toxicity range of a "normal" sludge and the determination of threshold limits criteria. Chemical-toilet sludge samples were spiked with two types and amounts of contaminants (zinc, phenol). Conservative criteria were used to detect abnormal toxicity with great reliability and avoid false positives (i.e., detecting abnormal toxicity in nonspiked sludge). Taken individually, the seed-germination test was the least discriminating toxicological method (detecting only 10% of the spiked samples); the bacterial-respiration test was relatively better (detecting 72% of the spiked samples). Using a limited battery of two toxicity tests (Microtox and respiration test), the identification of contaminated chemical-toilet sludge can be detected with good efficiency and possibly great reliability (more than 80% of the spiked samples). This proposed procedure is efficient, easy to apply, cost-effective, and very fast (an abnormal toxicity level can be determined within a few hours).