Hi K.M., this argument is tricky because there is no "since X, so therefore Y" structure. The way I went about looking for the conclusion was to contrapose the "only if" statement. In other words, I broke the argument down this way:

Would it be right for the government to do "X"?

Only if "Y"

However, evidence of "NOT Y"

Furthermore, more evidence of "NOT Y"

So when you push the contrapositive back, it leads to the conclusion that it is not right for the government to do "X. At this point, you can fill in what X is. This leads to the conclusion that it is not right for the government to abandon efforts to determine at what levels to allow toxic substances.

Hope this helped!