The herbicide paraquat, banned in over 70 countries, will remain legal in Australia despite Parkinson's groups, scientists and neurologists arguing there is a strong correlation between direct exposure and the incidence of the disease. The Australian Pesticides and Veterinary Medicines Authority (APVMA) announced its final decision on Tuesday following a decades-long review of the highly toxic paraquat and a related chemical, diquat. Both are widely used in Australian agriculture.