听力原文：A researcher at the University of Rochester in New York has found that workers exposed to high levels of lead on the job have an increased risk of dying from brain cancer. Epidemiologist Edwin van Wijngaarden looked at data about more than 300, 000 people over a nine-year period, comparing the kinds of jobs they had with their causes of death, and he saw a correlation. Mechanics are among the workers more likely to develop deadly brain tumors due to occupational lead exposure. He says, automobile and heavy equipment mechanics, painters and welders-who were more likely to be exposed to lead for longer periods of time-had even higher risks of developing brain cancer than workers unexposed to lead. Most research on lead has focused on its effect on children. Van Wijngaarden says not much is known about its impact over a lifetime. Wijngaarden found only 119 brain tumor deaths. He is continuing his research, looking now at patients who already have brain tumors, to see whether they have higher levels of lead in their bones than other patients. Who are NOT mentioned as people more likely to be exposed to lead?