As we enter the time of year that ticks and fleas are more prevalent, many of us are turning to our vets and pet stores to buy flea and tick collars. The prestigious environmental group, the Natural Resources Defense Council (NRDC), has urged regulators to remove from the market collars that contain propoxur and TCVP, or tetrachlorvinphos. The problem with the chemicals is that they can cause cancer and neurological damage. The NRDC’s scientists have also found that a startling amount of the chemicals are found on the pet after a pet collar is placed on the dog, and exceeding the Environmental Protection Agency’s own guidelines for what amounts of the chemicals acceptable for the brains of toddlers. For TCVP, after three days, 60 percent of the dogs and 40 percent of the cats had residue levels that would exceed the EPA’s acceptable level.