In a pilot study conducted on FoE's behalf, scientists from the Pesticide Research Institute examined flowering plants such as Salvia and Gaillardia, as well as pollinator-friendly fruits and vegetables such as tomato and squash, purchased from home improvement stores in the San Francisco Bay, Minneapolis/St. Paul, and Washington DC metropolitan areas. They found that of 13 composite samples (from 45 individual plants), seven tested positive for at least one neonicotinoid, with two testing positive for two residues, and a Gaillardia plant from Minnesota showing measurable levels of three different neonicotinoids.
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The reason for this, say the authors of the report, is that long before they reach stores, nursery plants are typically treated with systemic insecticides, which are absorbed through the roots or leaves of the plant and transported to various plant tissues. Although the sample size of this pilot study was relatively small, the authors argue that the high percentage of samples testing positive for neonicotinoids should prompt a wider study.