PEX and pesticides: bad mix?

Q:

In PEX Water Pipe: Is Copper on the Way Out? (FHB #180), Andy Engel says that “PEX is also susceptible to damage from certain oil- or solvent-based compounds and can allow these compounds to pass through the pipe and into the water.” He goes on to say never to bury PEX in contaminated soil.

Before we can pour a monolithic slab here, code requires us to treat the soil with some sort of pesticide to prevent termites. Wouldn’t treating the soil this way create contaminated soil? How should I address this issue?

A: Associate editor Daniel S. Morrison replies: At first glance, it would seem that pesticide-laden soil would qualify as contaminated. On second glance, it wouldn’t seem to be much of a problem because the insecticide comes in a plastic jug that is made of the same material PEX is made with. In fact, the chemical sits in a highly concentrated form in the plastic jug before it’s diluted for application. To find out more, I called a technical representative from Wirsbo, a PEX-tubing manufacturer, who said this: “While it is unlikely that the chemical itself will harm the tubing, in extreme cases, materials such as insecticides may penetrate the tubing and enter the water run. As a result, Wirsbo recommends that the tubing be sleeved 18 in. past the possible area of contact.”