[Environmental impact of tanning industry]

Airborne hydrogen sulphide was monitored continuously for 91 hours in the residential area of the Chiampo Valley in northern Italy, where about 150 tanneries are located; 74 air samples were taken to detect the environmental concentrations of solvents. Hydrogen sulphide concentrations obtained every 2.5 min in the residential area of Arzignano, the main town in the Chiampo Valley, were averaged over one hour. The mean values were plotted against time and wind direction: the tridimensional plot showed that the highest concentrations (over 300 ppb) were statistically detected between 10 a.m. and 12 a.m. with an east-southeast wind direction. About 40 tanneries are located over a distance of 1 km along this direction. The main causes of air pollution were the discharge of unhairing liquid and pickling operations in the factories, and the sewage system and waste water treatment plant. As regards solvents, a preliminary study showed that the 149 tanneries located in this area used about 17,700 tons/year of coating materials to finish about 40 million square metres of leather. Thirty more solvents were released into the atmosphere from these materials, the most important of which being: aromatic hydrocarbons (3,100 tons/year), acetates (2,800 tons/year), ketones (1,500 tons/year), alcohols (1,350 tons/year) and glycol ethers (520 tons/years). The average concentrations detected in the air were: 326 micrograms/m3 for aromatic hydrocarbons, 302 micrograms/m3 for acetates, 139 micrograms/m3 for ketones, 125 micrograms/m3 for alcohols and 16 micrograms/m3 for glycol-ethers. The cumulative concentration was more than 1 mg/m3 for 30% of the samples and more than 2 mg/m3 for 7%. The percentage of airborne solvents agreed well with that of solvents in the coating materials, thus demonstrating that most of these compounds originated from the tanneries.