The potential of trivalent and hexavalent chromium to induce and elicit allergic contact dermatitis and the degree of chromium exposure from leather products are reviewed. Chromium dermatitis is often due to exposure in the occupational environment, with cement being one of the most common chromium sources. However, consumer products such as chromium(III)‐tanned leather products are also an important source of chromium exposure. Apart from Cr(III), which is used for tanning, leather often also contains trace amounts of Cr(VI), which is formed by oxidation of Cr(III) during the tanning process. In a recent study of the Cr(VI) content of leather products bought on the Danish market, 35% of such articles had a Cr(VI) content above the detection limit of 3 p.p.m., ranging from 3.6 p.p.m. to 14.7 p.p.m. Leachable Cr(III) was detected at levels of 430–980 p.p.m. An examination of available dose–response studies showed that exposure to occluded patch test concentrations of 7–45 p.p.m. Cr(VI) elicits a reaction in 10% of the chromium‐sensitive patients. When reviewing repeated open exposure studies, it is seen that either exposure to 5 p.p.m. Cr(VI) in the presence of 1% sodium lauryl sulfate (SLS) or exposure to 10 p.p.m. Cr(VI) alone both elicit eczema in chromium‐sensitive patients. The eliciting capacity of Cr(III) has not been systematically investigated but, compared to Cr(VI), much higher concentrations are needed to elicit eczema.
Biomass, mainly consisting of an acidic polysaccharide produced by Zoogloea ramigera, has been used as an adsorbing agent in a continuous process for the recovery of metal. The adsorption of copper has been studied with respect to retention time, biomass concentration, and reaction pH, in order to determine the optimal conditions for copper recovery. The results indicate that the uptake of copper is rapid and efficient. About 0.17 g Cu is adsorbed per gram of biomass within 10 min. At high biomass concentrations, the total amount of copper removed from solution is high, but the specific amount of copper adsorbed to biomass is low. The biomass exhibits a higher adsorptive uptake at low concentrations.
Candida tropicalis S001 was grown on the lipid fraction of a protein-containing waste-water in order to (i) remove fat from the water, and (ii) produre yeast biomass for feed. The yeast cells were separated from the waste-water by sedimentation. Defatted wastewater was used for methane production and gave a yield of a 0.3 m 3 methane/kg reduced chemical oxygen demand. The maximum specific growth rate (/t~,ax) of C. tropicalis growing on waste-water fat at pH 4.0 was 0.35 h -l ; the fat content was decreased from 8 g/1 to about 0.1 g/1 within 24 h. In continuous culture a corresponding reduction was maintained at dilution rates up to 0.36 h -1. The effect on growth of pH, temperature and CO2 concentration was studied with triolein as the major carbon source. The /Z~ax was nearly constant (0.16 h -a) in the pH and temperature range of 3.2-4.0 and 30°-38 ° C, respectively; 10% CO2 was optimal for growth. Growth on triolein resulted in a biomass yield of 0.70 g dry weight/g fat.
An overview of the leather sector from the point of view of additives use is presented. In the first section, the general trends of the sector under concern in terms of world production and trade flows are reviewed, together with an overall description of the main characteristics of the production process including beamhouse (i.e., salting, soaking, unhairing, liming, deliming, pickling), tanning, posttanning (i.e., neutralization, bleaching, re-tanning, fatliquoring), and finishing operations. The second part is focused on the description of the different additive classes used to provide leather with the required functional characteristics and to facilitate and improve the production process as well, namely, fatliquoring agents, surfactants, coating agents (binders, lacquers), waterproofing agents, flame retardant agents, biocides, and dyes. Main compounds or compound families within each additive class are listed, and some related information regarding their function and environmental potential impacts is also included.
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