Ecotoxicity Assessment of Stabilized/Solidified Foundry Sludge ALBERTO COZ,* ANA ANDRE Ä S, AND A Ä NGEL IRABIEN Departamento de Ingenierı ´a Quı ´m ica y Quı ´m ica Inorga ´nica, Universidad de Cantabria, Avda de los Castros s/n, 39005 Santander, Spain The aim of this study is to evaluate the toxicity of the leachates from a foundry sludge and the derived products based on the stabilization/solidification (S/S) processes. Foundry sludge is an industrial hazardous waste containing inorganic and organic pollutants. The immobilization of the foundry waste has been performed using different S/S procedures based on cement or lime as binder agents and foundry sand fines, calcium-magnesium lignosulfonate, silica fume, activated carbon and black carbon as additives. The waste and stabilized/solidified derived products have been evaluated according to environmental considerations. The relation between the chemical composition and the ecotoxicity of the leachates has been studied in this paper. The ecotoxicity of the leachates has been related to the heavy metals and the organic pollutants by an empirical logarithmic linear expression. Different parameters of the logarithmic fitting have been obtained for the studied binder agents and additives allowing the establishment of a relationship between the S/S process and the ecotoxicity of the derived products. Results of this study have wide-ranging implications for immediate management strategies of waste with organic and inorganic pollutants in addition to application in long-term remediation efforts. Introduction Some biological tests have been developed for the technical evaluation of the ecotoxicity of waste with many pollutants and waste of complex character (organic and inorganic pollutants) by means of a single bioassay. The advantage of the biotests is that the toxicityofthe waste stream is measured andmaybecompared.Thus,thetoxicityofthecontaminants is estimated, taking into account bioavailability and syner- gistic or antagonistic effects. There are some basic requirements for ecotoxicological testing(1).It must be representative,reproducible,and simple to enable the frequent control of effluents by short-term testing and must be cost-effective. Several test system hierarchies have been considered for these purposes (1): toxicity test with simple species (e.g., fish, daphnia, algae, and bacteria) or suborganism test systems (e.g., fish cell tests). However, there is not any test system that completelyfulfillsthe above-mentioned criteria. For example, toxicity tests with single organisms cannot perfectly fulfill the expectations for ecosystem relevance. Whereas such a test is representative for the same species and related organisms, a single species test does not reflect basic interactions in the ecosystem. There is a need to develop fast,robust,and peer-reviewed techniques based on biochemical mechanisms to assist toxicologicalparameters.Bacteria and enzyme systemshave great potential; certain species of marine luminescent bacteria, in particular Vibrio fischeri (formerly known as Photobacterium phosphoreum ), are useful surrogates for toxicological assessment (2). In the literature, different biotests (fish, daphnia, algae, and luminescent bacteria) have been compared (1, 3-6). The bacterialbioluminescence assayhas been considered in this paper because it is a rapid, robust, highly sensitive method. The results show reproducibility, they are cost- effective, and the reference limits are given in the Spanish Regulations. Furthermore, the bioluminescence assay has a worldwide application and standarization for regulatory purposes; it is preferred over other bacterial screening techniques. This work takes a foundry sludge generated from wet cleaning of gases and listed as hazardous waste in the European Waste Catalogue 2001, identifying this waste with the code 100213*(7). Table 1 shows the results of the waste characterization (8, 9).Accordingto the Spanish Regulations, based on the inhibition of the luminescence of a marine bacteria (limit 3000 mg/L) (10), the waste is ecotoxic with EC50 lower than 1000 mg/ L. EC50 (mg/ L) is expressed as the effective concentration oftoxicant that causesa 50%decrease in the light output.The ecotoxicityofthe waste maybe related to organic compounds (phenols) and inorganic elements (zinc) as the main pollutants. These pollutants and the high proportion of water in the sludge make it difficult to handle and to manage the waste. In previous studies (9, 11), several immobilization pro- cesses have been developed in order to obtain a waste for disposal. Stabilization/solidification (S/S) processes were applied because theyare known techniques for the treatment ofindustrialwaste and theyare technicallyand economically feasible. In this work, lime and cement are used as binder agents and foundry sand fines; calcium -magnesium ligno- sulfonate is used as a superplasticizer; and silica fume, activated carbon, and black carbon are used as additives. Leaching tests have been carried out in order to evaluate the stabilized/solidified derived products following the European Regulation (12). The chemical parameters were the phenol index and the zinc concentration. Biolumines- cence tests with V. fischeri and Microtoxstandard tests have been carried out to determine the ecotoxicityofthe leachates according to the Spanish Regulations (10) and to check the influence of the chemical composition on the ecotoxicity. Although many papers have reported the leaching be- havior of heavy metals and organic pollutants in waste and derived products (13-19),few results have been reported on the ecotoxicityofS/Sproducts and the relationship between ecotoxicity and chemical composition (3, 4, 20, 21). Cor- relations between parameters have been mentioned (22- 24),but the cumulative effect ofinorganic (zinc)and organic (phenols)pollutants has not been described in the literature. The experimental results allow us to formulate a cor- relation relatingecotoxicityofthe stabilized/solidified derived products with the chemical composition, both organic (phenols) and inorganic (zinc). These relations are useful in optimizingthe S/Sprocesses for hazardous waste treatment before disposal. *Corresponding author phone: +34-942201359; fax: +34- 942201591; e-mail: coza@unican.es. Environ. Sci. Technol. 2004, 38, 1897-1900 10.1021/es034913f CCC: $27.50  2004 American Chemical Society VOL. 38, NO. 6, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 1897 Published on Web 02/13/2004