The combined actions of chemical agents (lead and/or cadmium) and a physical agent (noise) was studied in laboratory rats. There were nonhistological effects that were first observed in the experimental groups such as fur discoloration (brown pigmentation), ruffled fur, the absences of fecal droppings at certain times during the noise exposure period, and a decrease in the total weight gained. In addition to the nonhistological effects, the combined effects of low level white noise, with a sound pressure range of 68-72 dB(A) and low level lead and/or cadmium produced substantial histological changes in the hearts of the experimental rats which were characterized by marked hypertrophy, muscle fiber fragmentation and sarcolysis. The analysis of variance showed that the decrease in the total weight gained in the experimental groups compared to that in the control groups was due to the additive effect of noise combined with lead and cadmium. Interestingly, the analysis of variance on the histologic changes in the hearts showed a synergistic effect when noise was combined with lead and cadmium or combined with lead or cadmium alone. This effect is clearly seen by comparing the number of rats in the experimental groups that developed hypertrophy, muscle fiber fragmentation, and sarcolysis in their myocardia to the corresponding number in the control groups.
