Accumulation makes the... what rhymes here?

In some cases it still is, but we need to emphasize the exceptions, which can be rather serious.

For example, we can hardly "dilute" CFCs or CO2 any more than we did, by putting them into a whopping 5.15×10^18 kg of the entire atmosphere of the Earth. Yet both still cause bad things, because there's no (sufficient) process to break them down or move them to a safe state.

The dosage makes the poison - but if it sticks around in the body dilution may slightly alleviate effects but at the cost of more widespread buildup. This is out of my field so I'm not certain if that's a concern here.