help, pvc mess

One of the solvents used in that type of cement is tetrahydrofuran (THF) which is toxic. Fumes may have been trapped inside the overflow & mixed with the water when you started it up. There are other solvents as well that are used that are also toxic. The cement skins over rapidly & if there were any thick areas that oozed out from the joint they may not have been totally dried leaving the material to leech into the water. Might be a good idea to run some carbon to filter out the organics.