A survey of five regional hospitals in 1983 found that over seven per cent of total poisoning cases were occupationally related. In 1984, a survey showed that the average lead level in the blood of workers at a Thai battery plant was in the range of 12 to 48 milligrammes per 100 millilitres of blood - around 480 times greater than world health standards. A study by the Thai ministry of public health showed that the incidence of environmentally related health cases increased from 2 cases per 100,000 people in 1978 to 8.88 per 100,000 in 1987.