A chemical that’s used as an agricultural fungicide causes irreversible damage to human tumour-fighting cells, says new research being reported by New Scientist. A team led by Margaret Whalen, a biochemist at Tennessee State University, exposed human killer T cells-a type of immune cell that destroys cancerous and other abnormal cells-to Triphenyltin, or TPT. They then measured the cells’ potency against isolated human leukemia cells, the report says. After one hour of exposure, the killer T cells lost between 50 and 60 per cent of their destructive powers. But what’s more important, the article says, even after the cells were no longer exposed to the chemical they could not regain their previous killing power. Whalen says it is not clear yet whether there is a real risk to people working with the chemical. She suspects that agricultural workers are exposed to lower levels in the field than those she used in the lab. “But it’s hard to know what real-life levels of phenyltins are,” she says.