New Delhi/London : The pesticide that killed 23 Indian schoolchildren last week is a nerve poison banned by many countries because of what the World Health Organisation (WHO) describes as its “high acute toxicity”. As early as 2009, the United Nations health agency urged India to consider a ban on the pesticide monocrotophos — the substance said by a magistrate investigating the deaths to be the cause of the poisoning. It had also warned that in India — against strong international health warnings — many pesticide containers are not thrown away after use but recycled and used for storing water, food and other consumables. In last week’s case in Bihar, the children fell ill within minutes of eating a meal of rice and potato curry in their one-room school. They were vomiting and convulsing with stomach cramps — symptoms that experts say would be common in poisoning with such a toxic chemical. The lunch was part of India’s mid-day meal scheme, which aims to tackle malnutrition and encourage 120 million poor children to attend school. It had already drawn widespread complaints over food safety. An initial forensic investigation found the Bihar children's meal had been prepared with cooking oil that contained monocrotophos.