<Tr> <Th> Exposure </Th> <Th> Category 1 </Th> <Th> Category 2 </Th> <Th> Category 3 </Th> </Tr> <Tr> <Td> Acute </Td> <Td> ≤ 1.0 mg / L </Td> <Td> ≤ 10 mg / L </Td> <Td> ≤ 100 mg / L </Td> </Tr> <Tr> <Td> Chronic </Td> <Td> ≤ 1.0 mg / L </Td> <Td> ≤ 10 mg / L </Td> <Td> ≤ 100 mg / L </Td> </Tr> <P> Note: A category 4 is established for chronic exposure, but simply contains any toxic substance which is mostly insoluble, or has no data for acute toxicity . </P>

What is the difference between a toxic chemical and a harmful chemical