If a crime is committed, pollution or killing of someone's property, then simply send the case to a court house not the congress. There were laws already in place that says you cannot damage (pollute) someone else's property without just compensation. Well why is it necessary to add another law? The first one was never implemented and thus you got the improper use of DDT. I live in a country that DDT is okay, and we have no problems because we use it properly. There are many chemicals that are much more dangerous than DDT and less effective.
Your last question summarizes it quite well; if they are violating the law then they are to be prosecuted. Now the problem is that we have too many laws. The only laws that are really necessary are to protect your life, liberty and property. Upon any point that either of those three confronts with someone else's life, liberty and property, then a law should be in place to settle/prevent disputes. So in the case of GMOs, if someone's corn pollinates my conventional corn with a GMO gene, they have caused damage to my property. As for soybeans, they don't cross pollinate so there is no problem there.