The U.S. EPA’s scientific advisers asked the agency to delay finalizing its decision not to set standards for the toxic chemical perchlorate in drinking water, saying the model its decision was based on may be flawed. “Given perchlorate’s wide occurrence and well-documented toxicity to humans, the [Science Advisory Board] strongly believes that there must be a compelling scientific basis to support a scientific determination not to regulate perchlorate as a national drinking water contaminant,” the board wrote to the EPA last week.