A popular herbicide used widely in coastal regions of Australia has been found at dangerous levels in the Great Barrier Reef, posing a toxic threat to the world’s largest coral reef system. The chemical Diuron, which is used largely by sugar cane farmers along the Queensland coast, was found at levels 55 times higher than safety standards in creeks that drain into the reef, and at levels 100 times the safe standards in the reef itself, according to a new report by the World Wildlife Fund. After a decade-long review, the Australian government on Tuesday announced it would continue a suspension of the chemical except in the country’s tropical regions. A decision on a permanent ban will be made by November, the Australian Pesticides and Veterinary Medicines Authority said. In a recent report, the Great Barrier Reef Marine Park Authority called a decline in the quality of water in catchment areas one of the greatest threats facing the reef. Nick Heath, the WWF freshwater and reef coordinator, said the widespread use of the chemical and the length of time it persists in the environment pose a significant threat.