Of course the best course when experimenting with materials used in a manner different from original approved uses is, as Janie said, to do your research. PVC comes in different formulations, some of which are safer than others in terms of chemical leaching. It's used in household plumbing for drinking water in many places. It's used in many growers' hoop houses, too. Many have found approved grades of CPVC pipes to be safer than the old metal plumbing materials, depending upon whether lead and other hazardous materials are leaching from pipes and solder, and what sort of water characteristics are involved (see link to Maine Cooperative Extensioninformation on corrosive water.) Here's a link for those interested in researching pvc safety in regard to use with drinking water and gutter gardens, etc.: National Sanitation Foundation (NSF)
Following from that page, I found this:

"PVC, CPVC, PEX, and Other Plastic Plumbing Materials - Plastic plumbing has been used for potable and non-potable water applications since the 1950s. Initially, there were many concerns about these products potentially leaching harmful chemicals into the water. To ensure that the public's health was protected, independent standards were quickly developed which established strict guidelines for these products.

Today, plastic plumbing products designed for potable water applications are usually designated with either "NSF-PW" or "NSF-61" to indicate that the product complies with the health effects requirements of NSF/ANSI Standard 61 for materials designed for contact with potable water. This standard also establishes similar guidelines for other plumbing materials, including copper tubing. If your pipe is not coded with one of these designations or if it is designated with an alternative code such "NSF-DWV," it is probably not meant for potable water applications and should not be used for such purposes."
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Perhaps one could learn more regarding the safety of PVC gutter materials by sending an email to the NSF International (info@nsf.org).