Assessment of the application of an ecotoxicological procedure to screen illicit toxic discharges in domestic septic tank sludge

An innovative screening procedure has been developed to detect illicit toxi c discharges in domestic septic tank sludge hauled to the Montreal Urban Co mmunity wastewater treatment plant. This new means of control is based on a n integrative approach, using bioassays and chemical analyses. Conservative criteria are applied to detect abnormal toxicity with great reliability wh ile avoiding false positive results. The complementary data obtained from t oxicity tests and chemical analyses support the use of this efficient and e asy-to-apply procedure. This study assesses the control procedure in which 231 samples were analyze d over a 30-month period. Data clearly demonstrate the deterrent power of a n efficient control procedure combined with a public awareness campaign amo ng the carriers. In the first 15 months of application, between January 199 6 and March 1997, approximately 30% of the 123 samples analyzed showed abno rmal toxicity. Between April 1997 and June 1998, that is, after a public he aring presentation of this procedure, this proportion dropped significantly to approximately 9% based on 108 analyzed samples. The results of a 30-month application of this new control procedure show th e superior efficiency of the ecotoxicological approach compared with the pr eviously used chemical control procedure. To be able to apply it effectivel y and, if necessary, to apply the appropriate coercive measures, ecotoxicol ogical criteria should be included in regulatory guidelines.