TOXICITY OF Sb AND Cu IN SEWAGE SLUDGE TO TERRESTRIAL PLANTS (LETTUCE, OAT, RADISH), AND OF SLUDGE ELUTRIATE TO AQUATIC ORGANISMS (DAPHNIA AND LEMNA) AND ITS INTERACTION

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Abstract

Antimony (Sb) and Copper (Cu) are two metals of major concern in sewage sludge. Antimony because its use in society is increasing and this might lead to increased Sb concentrations in sludge. Copper because its total volume in use in society is large and because of corrosion from water pipes it is most difficult to reduce the Cu concentrations in sludge. Fresh digested sewage sludge was spiked with Cu or Sb and the sludge was cultivated with oat (Avena sativa), lettuce (Lactuca sativa) or radish (Raphanus sativus). Elutriates from the cultivated sludge were tested for toxicity with Lemna minor (7-d growth) and Daphnia magna (48 h immobility). Before cultivation the elutriates were toxic to Lemna and Daphnia due to high concentrations of ammonia (NH3) and nitrite (NO2-). Cultivation decreased the concentrations of both NH3 and NO2-, thereby reducing the impact of these compounds in the toxicity tests. Cultivation also decreased the metal concentrations and pH. Daphnia magna was the most sensitive test organism in this study with a 48 h EC50 of 1130 mg Cu kg-1 dry wt and 5 mg Sb kg-1 dry wt in elutriates from sludge cultivated with oat. In sludge cultivated with radish the 48 h EC50 was 1700 mg Cu kg-1 dry wt and 22 mg Sb kg-1 dry wt. The effect of Cu could be predicted by pH and Cu concentration in the elutriate, but the effect of Sb could not solely be explained by its concentration in the elutriate.

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