Wastewater toxicity of tannin- versus chromium-based leather tanneries in Marrakesh, Morocco

The toxicity of leather tanning wastewater from a traditional tannery (TT), which is based on vegetable tannin (VT), was compared with wastewater from a tannery combining the use of chromium- based tanning (CT) with VT- based tanning operations. Wastewater samples from a TT and a CT plant as well as from five sewer sampling points were collected in Marrakesh, Morocco, and the concentrations of VT and some selected inorganics were measured. A set of bioassays were used to test wastewater toxicity in sea urchin (Paracentrotus lividus) embryos and sperm, in Daphnia magna, and in marine microalgae (Dunaliella tertiolecta). Toxicity end points included: (1) developmental defects, embryonic mortality, sperm fertilization success, and offspring damage in sea urchins; (2) D. magna immobilization; and (3) algal growth rate inhibition. Toxicity tests on TT and CT effluents (TTE and CTE) were run at dilutions ranging from 0.1% to 2% (sea urchins and algae) or up to 12% in D. magna. Parallel bioassays were run on VT extract (VTE) at nominal tannin concentrations ranging from 0.1 to 10 mg l - 1. The results showed higher toxicity of CTE compared with TTE. CTE toxicity in sea urchins and algae showed concentration- related trends, whereas TTE exerted hormetic effects at levels of 0.1% to 0.2% and toxic effects at levels 1%. The same trends were observed for VTE, suggesting a prevailing role of tannin in TTE-associated effects. The moderate wastewater toxicity of VT-based tanneries might prompt interest in the VT tanning process. An established body of evidence has associated the chromium-based leather tanning (CT) industry with environmental and occupational health concerns, which has been reviewed by several investigators (Losi et al. 1994; Battista et al. 1995; Chattopadhyay et al. 1999; Chandra et al. 2004; Meric, et al. 2005; Mwinyhija et al. 2006; Nath et al. 2005; Otero et al. 2005; Riva et al. 2005; Tagliari et al. 2004; Zhou et al. 2005). Unlike the CT industry, scanty information is available regarding the environmental impact of the traditional leather industry based on the use of vegetable tannin ( VT) and of a set of natural organic agents ( Anonymous 1974; De Nicola et al. 2004, 2006). Wastewater from VT- based tanneries is The toxicity of leather tanning wastewater from a traditional tannery (TT), which is based on vegetable tannin (VT), was compared with wastewater from a tannery combining the use of chromium-based tanning (CT) with VT-based tanning operations. Wastewater samples from a TT and a CT plant as well as from five sewer sampling points were collected in Marrakesh, Morocco, and the concentrations of VT and some selected inorganics were measured. A set of bioassays were used to test wastewater toxicity in sea urchin (Paracentrotus lividus) embryos and sperm, in Daphnia magna, and in marine microalgae (Dunaliella tertiolecta). Toxicity end points included: (1) developmental defects, embryonic mortality, sperm fertilization success, and offspring damage in sea urchins; (2) D. magna immobilization; and (3) algal growth rate inhibition. Toxicity tests on TT and CT effluents (TTE and CTE) were run at dilutions ranging from 0.1% to 2% (sea urchins and algae) or up to 12% in D. magna. Parallel bioassays were run on VT extract (VTE) at nominal tannin concentrations ranging from 0.1 to 10 mg l(-1). The results showed higher toxicity of CTE compared with TTE. CTE toxicity in sea urchins and algae showed concentration-related trends, whereas TTE exerted hormetic effects at levels of 0.1% to 0. 2% and toxic effects at levels &GE1%. The same trends were observed for VTE, suggesting a prevailing role of tannin in TTE-associated effects. The moderate wastewater toxicity of VT-based tanneries might prompt interest in the VT tanning process known to inhibit the activity of microorganisms during biologic oxidations in tertiary effluent treatment because of high levels of tannins and other chemicals, and two studies have reported processes aimed at optimizing the environmental performance of VT- based leather tanning operations (Panizza & Cerisola 2004; Saravanabhavan et al. 2004). We reported previously that water extracts of Acacia tannin, used in leather- tanning operations, induced a nonlinear concentration- related effect, with a shift from hormesis ( Calabrese & Baldwin 2002) to toxicity at VT levels ranging from 0.3 to 30 mg l(-1) (De Nicola et al. 2004). To the best of our knowledge, however, no information is available on the toxicity of wastewaters from VT- based tanneries at concentrations that may mimic the environmental dilution of wastewater in sewage systems. Hence, also unknown is any comparison between wastewaters of VT versus CT tanneries. In the attempt to gain knowledge regarding these unsolved questions, this study was aimed at comparing the toxicities of wastewater from VT versus CT leathertanning facilities employing a set of bioassays measuring sea urchin Paracentrotus lividus early development, Daphnia magna immobilization, and marine microalga Dunaliella tertiolecta growth rate. Wastewater from VT and CT tanneries was collected in Marrakesh, Morocco, and bioassay results pointed to sharp differences in wastewater toxicity for VT versus CT tanneries.