Fig. (3) Average optical density at 600nm for samples over 216 h fermentation in the detoxification of leather dust using B. subtilis SA-6. Nutrient broth (NB), Nutrient broth + B. subtilis(NBBS), Nutrient broth + Chromium (NBCR), Nutrient broth + Leather dust (NBLD), Nutrient broth + B. subtilis+ Chromium (NBBSCR), Nutrient broth + B. subtilis+ Leather dust (NBBSLD), Nutrient broth + B. subtilis+ Chromium + Leather dust (NBBSCRLD.