This does not weaken the argument, because it doesn’t give us any reason to doubt the representative’s implied conclusion. Whether the testing delays the entry of substances onto the market tells us nothing about chemical safety standards.

This does not weaken the argument. The representative says that the chemicals are safe due to testing requirements, and like (D), how long they’ve been leaking has no relevance to that claim.

This weakens the argument by casting doubt on whether all the chemicals in the company’s “long-established” dump would actually meet current safety requirements. This claim makes it totally possible that there are many dangerous untested chemicals in the dump.

This does not weaken the argument, because like (B), the amount of likely exposure isn’t really the issue here. The representative’s claim is that the chemicals are safe, not that they’re potentially unsafe but diluted. This doesn’t address the chemicals’ actual safety.

This does not weaken the argument. Whether or not the river water is murky, or what other substances are in the river, is totally irrelevant to the issue of chemical safety. This just does not affect the argument at all.