<P> In 2013 lead is believed to have resulted in 853,000 deaths . It occurs most commonly in the developing world . Those who are poor are at greater risk . Lead is believed to result in 0.6 % of the world 's disease burden . People have been mining and using lead for thousands of years . Descriptions of lead poisoning date to at least 2000 BC , while efforts to limit lead 's use date back to at least the 1500s . Concerns for low levels of exposure begin in the 1970s with there being no safe threshold for lead exposure . </P>
<P> In 2013 lead is believed to have resulted in 853,000 deaths . It occurs most commonly in the developing world . Those who are poor are at greater risk . Lead is believed to result in 0.6 % of the world 's disease burden . People have been mining and using lead for thousands of years . Descriptions of lead poisoning date to at least 2000 BC , while efforts to limit lead 's use date back to at least the 1500s . Concerns for low levels of exposure begin in the 1970s with there being no safe threshold for lead exposure . </P>
when was it discovered that lead was poisonous
when was it discovered that lead was poisonous
at least 2000 BC
at least 2000 BC