Insect-induced plant galls expose hard-to-detect belowground contaminants

Detecting belowground chemical contamination is challenging due to heterogeneity of the subsurface and limited monitoring capabilities associated with energy-intensive, intrusive, costly sampling techniques. Recently, chemical analysis of vascular plant tissue has been used as an aboveground “phytoscreening” tool to detect belowground contaminants. To date, phytoscreening has used tree cores to detect subsurface contaminants, which has several drawbacks. First, inorganic contaminants such as heavy metals can accumulate in tree cores, however, volatile organic compounds are typically stored for a shorter time. Additionally, core sampling can negatively impact tree health. Unfortunately, the literature suggests that phytoscreening of aboveground tissues such as leaves, fruits, and twigs trend towards lower concentrations than tree cores. Lastly, trees may be unavailable for sampling at all contaminated sites, especially in urban areas. Thus, there is a need to develop core-less phytoscreening methods sensitive to the detection of a wide-range of subsurface contaminants that incorporate the use of plants other than trees (vines, shrubs). Here, we document that insect-induced galls–tumor-like outgrowths commonly found on vascular plants that contain high concentrations of nutrients–can also act as sinks for belowground chemical contaminants including inorganic heavy metals, semi-volatile organic compounds (1-4, Dioxane), and volatile organic compounds (TCE) in similar or greater concentrations than other aboveground plant tissues. Given that they are found on most vascular plant species, easy to collect en masse, and common in urban areas, galls may be a powerful tool when assessing sites for belowground chemical contamination, especially where detecting low concentrations is critical.