ABSTRACT

Various species of microbes present in marine environments are responsible for the corrosion of metals. The objectives of this work were to analyze both the growth of some marine microorganisms in the presence of Pb, and biocorrosion in a dynamic system. Carbon steel AISI 1020 coupons were inserted in a PVC (“loop”) system, with the goal of simulating natural conditions, and exposed to seawater, using lead concentrations of 25 to 50 ppm. For fifteen days, the planktonic and sessile populations—aerobic, anaerobic, and sulfate-reducing bacteria (SRB)—were quantified through the MPN technique. The corrosion rate was determined by the weight loss of the coupon. The coupons were also microscopically analyzed, and the percentage pit/cm² was determined using the GLOBAL Lab IMAGE Program. The resistance of the planktonic bacteria to the Pb was dependent upon the bacterial group. The SRB were more sensitive to the presence of lead, demonstrating mortality proportional to the metal concentration. After 15 days, a larger number of sessile bacteria was determined on the biofilm exposed to 25 ppm of Pb, and a reduction of the number of cells in 50 ppm, especially for the SRB. The corrosion rate of the coupons exposed to 25 ppm of Pb was elevated, much higher than that of those exposed to 50 ppm. The percentage pits/cm² was 5.64 and 2.66, respectively, for 25 and 50 ppm of lead. These results suggest that the rise in lead concentration inhibited the growth of SRB, and the corrosion was directly affected by the activity of the SRB.