To allay public concern about chemicals that are leaking into a river from a chemical company' s long-established dump, a company representative said, "Federal law requires that every new chemical be tested for safety before it is put onto the market. This is analogous to the federal law mandating testing of every pharmaceutical substance for safety. " Which one of the following, if true, most seriously weakens the representative's implied argument that the public need not be concerned about the leak? ['Leakage from the dump has occurred in noticeable amounts only in the last few months.', 'Before the federal law requiring testing of nonpharmaceutical chemicals went into effect recently, there were 40, 000 such chemicals being manufactured, many of them dangerous.', 'When pharmaceutical substances are tested for safety pursuant to federal requirements, a delay is imposed on the entry of potentially lifesaving substances onto the market.', 'The concentration of chemicals leaking into the river is diluted, first by rainwater and then by the water in the river.']