The inhibitor effect of copper sulphate on microbial glucose degradation in red latosol soil

Microcalorimetry has been used in a series of experiments to study the inhibitory effect caused by copper sulphate on soil microbial activity. This activity was stimulated by addition of 6.0 mg of glucose and 6.0 mg of ammonium sulphate under a controlled humidity of 53% in a red Latosol soil sample of 1.50 g. Power-time curves were recorded for increasing amounts of the inhibitor, varying from zero to 6.19 mg. The curves showed a decrease of the maximum amplitude of the experimental curve, which shifted to longer times. Increasing masses of copper sulphate caused a decrease of the original thermal effect to reach a null value at 6.19 mg of inhibitor. The results relating the dependence of the maximum amplitude of the peak time with the considered pollutant mass, were fitted to a kinetic model in an attempt to establish the inhibitory effect of copper sulphate. In this conditions, the data were adjusted to a first power order model for the degradation of glucose. In the absence of inhibitor the consumption of glucose by the microorganisms is about 10% of the initial mass and decreases with the increase of the copper added to the soil sample.