The state of Louisiana has reported 415 cases of health problems linked to the spill, with symptoms including sore throats, irritated eyes, respiratory tract infections, headaches and nausea.
But Bernard Goldstein, an environmental toxicologist and professor at the University of Pittsburgh, said the US government's method of collecting health data on the workers is flawed.
For instance, a major study of response workers by the National Institute of Environmental Health Sciences was not funded until six months after the spill, a critical delay that affects both the biology and the recall ability of the workers.
"It is too late if you go six months later," he told AFP.
Benzene, a known carcinogen present in crude oil, disappears from a person's blood within four months, Goldstein said.
Polycyclic aromatic hydrocarbons, or PAHs, are pollutants that can cause genetic mutations and cancer. They are of particular interest in studying long-term health, but without a baseline for comparison it is difficult to know where they came from -- the oil spill or somewhere else in the environment.
"They last in the body for a longer period of time but they also get confounded by, if you will, obscured by, other sources of PAHs," like eating barbecued meat or smoking cigarettes, said Goldstein.
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