If you're looking for good quantitative results for low-ppb metals (known species), you probably want ICP-AES.
In the case of the chemical involved in this spill, it turns out to be a cyclic organic alcohol for which relatively little toxicity data was available. The CDC had to move fast to come up with a permissible exposure number based on limited LD50 testing in rats. Once they provided that number, the local officials were able to monitor the situation and determine when the water was safe to use.
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