Comparative evaluation of the potential noxiousness in domestic sludge used in agriculture and in commercial fertilizers

The noxiousness of actual sludge collected in eight water treatment plants around the city of Toulouse, France, was evaluated using a biological test based on the growth rate of cultured human cells, Results were compared wit h those obtained from 18 fertilizers and culture supports that are commerci ally available in Gardening shops. Surprisingly, it was found that sludge e xtracts, at low concentrations (below 5 g of dry material/liter), were impr oving the cell growth rate, which suggests the presence of useful oligoelem ents. At higher concentrations, a noxious effect, expressed as inhibition o f cell growth, was observed. However, this negative effect was of the same order of magnitude as that obtained, under the same experimental conditions , with commercial garden fertilizers which are available and used without a ny restriction. It is concluded that discarding the sludge, after submissio n to the biological test, in controlled amount as an agricultural fertilize r should not be hazardous to the environment. (C) 2000 Academic Press.