Pb low doses induced genotoxicity in Lactuca sativa plants

Soil and water contamination by lead (Pb) remains a topic of great concern, particularly regarding crop production. The admissible Pb values in irrigation water in several countries range from ≈0.1 to ≈5 mg L^-1. In order to evaluate putative effects of Pb within legal doses on crops growth, we exposed Lactuca sativa seeds and seedlings to increasing doses of Pb(NO₃)₂ up to 20 mg L^-1. The OECD parameter seed germination and seedling/plant growth were not affected by any of the Pb-concentrations used. However, for doses higher than 5 mg L^-1 significant DNA damage was detected: Comet assay detected DNA fragmentation at ≥ 5 mg L^-1 and presence of micronuclei (MN) were detected for 20 mg L^-1. Also, cell cycle impairment was observed for doses as low as 0.05 mg L^-1 and 0.5 mg L^-1 (mostly G₂ arrest). Our data show that for the low doses of Pb used, the OECD endpoints were not able to detect toxicity, while more sensitive endpoints (related with DNA damage and mitotic/interphase disorders) identified genotoxic and cytostatic effects. Furthermore, the nature of the genotoxic effect was dependent on the concentration. Finally, we recommend that MN test and the comet assay should be included as sensitive endpoints in (eco)toxicological assays.