What chemical elements from sewage attack crops?

Hello,
I am currently conducting a study about the negative impacts of sewage water that contaminates the irrigation system of crops, particularly bananas.

This is for a study I have to do for uni. I plan on going on-site and asking experts in the region, but as part of my preliminary research, could you please tell me in general which compound has been found to specifically damage crops or make them sick?

To put it more clearly, it’s not enough for me to say " “the sewage harms the crops”. I’d like to know what specifically in the sewage harms them.

Thank you in advance, help of any kind is appreciated!

you could contact Mr. Ravi Savant of Prerana Laboratories PH. 09822555632

he sells Sewage Water Testing Kit

http://www.watertestingkits.co.in/water-testing-kits.html