Spatial analysis of uptake and accumulation of metalaxyl, spirotetramat, and spirotetramat-enol in maize at the micrometer scale using HPLC-HRMS and MALDI-MSI

Plant protection products (PPPs) are applied on a global scale in vast quantities, which results in elevated concentrations of active ingredients in the soil pore water. Depending on their fate, these PPPs have the potential to pose a threat to the environment and surrounding ecosystems. PPPs that are dissolved in the soil pore water are available for uptake by crop roots, which can lead to bioaccumulation in different plant parts, depending on the characteristics of the PPPs used. The quantity of the active ingredients absorbed and the fate of these substances within the plant are contingent upon the specific uptake routes. We exposed young maize plants to metalaxyl and spirotetramat or its metabolite spirotetramat-enol in a hydroponic setup. We investigated the root uptake and subsequent translocation to shoots via Orbitrap high resolution mass spectrometry. Furthermore, MALDI mass spectrometry imaging (MSI) was employed to elucidate the accumulation of metalaxyl and spirotetramat in specific organs of maize on a micrometer scale. This study demonstrates that both PPPs are readily taken up via the roots of maize plants yet differ significantly in their distribution. MALDI-MSI is particularly important to get a better mechanistic understanding. Thus, metalaxyl accumulates in the xylem and is predominantly found in the leaves whereas spirotetramat accumulates in the root epidermis. These new insights are helpful for the environmental impact assessment and MALDI-MSI an exciting new aspect to consider in environmental analysis.