PROVIDENCE — Seems as soon as the daffodils come up, so do those little white and yellow flags — themselves harbingers of spring — announcing that lawn chemicals have been applied.

In Providence, the area around Blackstone Boulevard, where the lawns are, is where ecoRI News found the highest concentration of lawn-chemical signs. But all that lush green that sprawls in front of tidy, brick homes has a dark side.

The Natural Resources Defence Council, after several years examining federal government data and interviewing key officials, has determined that the government has allowed the majority of pesticides onto the market without a full set of toxicity tests, using a loophole called a conditional registration. In fact, as many as 65 percent of more than 16,000 pesticides were first approved for the market using this loophole.

Two of the most common pesticides, glyphosate used in Roundup and 2,4-D in Weed B Gon Max, have been linked to a slew of health issues such as autism, ALS, developmental disorders and cancer. Lawn chemicals have also been shown to harm pets, and they run into Narragansett Bay, where they can disrupt the fragile marine ecosystem.