Agricultural chemicals:

increase food production
have caused human deaths
are sometimes difficult to destroy
all of the above

Agricultural chemicals  

increase food production have caused human deaths are sometimes difficult to destroy Explanation: Though there are agricultural chemicals that boost the yield, they are also responsible for some human deaths. These chemicals contain various elements that stay intact for a long time and are apparently undestroyable. These elements become a part of the food chain and keep flowing through the food cycle. Excess quantities of these elements prove fatal.

Ba rock that formed 1,400 million years ago!