The world's best-selling weedkiller, and a genetically modified maize resistant to it, can cause tumours, multiple organ damage and lead to premature death, new research published today reveals. In the first ever study to examine the long-term effects of Monsanto's Roundup weedkiller, or the NK603 Roundup-resistant GM maize also developed by Monsanto, scientists found that rats exposed to even the smallest amounts, developed mammary tumours and severe liver and kidney damage as early as four months in males, and seven months for females, compared with 23 and 14 months respectively for a control group.