Investigating the Toxic Impacts of Various Arsenic Compounds on Hydroponics Lettuce (Lactuca sativa L.): Biomass, Arsenic Accumulation and Species Distribution

Abstract

The risks resulted from organic and inorganic arsenic have attracted global attentions. In the study, the toxic effects of different arsenic compounds on lettuce (Lactuca sativa L.), including arsenite (As(III)), arsenate (As(V)), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), p-arsanilic acid (p-ASA) and roxarsone (ROX), were evaluated at various concentration levels. The results showed that low concentrations (5.00 µM) of arsenic compounds might promote lettuce growth, while high concentrations of arsenic species (25.00 µM for As(III) and DMA, and 150.00 µM for As(V), MMA, p-ASA, and ROX) can lead to significant reductions in lettuce biomass (up to 79%), chlorophyll (up to 34%) and nitrogen contents (up to 24%). Moreover, the arsenic compounds induced oxidative stress, resulting in significant increases in hydrogen peroxide (H₂O₂) (up to 132%), superoxide (O₂⁻) (up to 145%), and malondialdehyde (MDA) (up to 68%) in the treatment groups compared to the controls. In particular, ROX and p-ASA increased H₂O₂ levels by 45% and 62%, and boosted O₂⁻ levels by 76% and 127%, respectively, despite their lower toxicity levels compared to inorganic arsenic (i-As). Accumulation of arsenic in the lettuce roots and leaves were observed. Roots showed stronger accumulation capacity of arsenic than leaves, with a root-to-leaf ratio of total As varying from 9.11 to 1.49 × 10³. Notably, i-As including As(III) and As(V), were detected in the lettuce leaves of groups treated by organic arsenic compounds, with the concentration of 1.09 µg/g for p-ASA and 0.37 µg/g for ROX, respectively. Overall, the study demonstrates that although organic arsenic compounds like ROX and p-ASA exhibit lower toxicities than i-As, they can contribute to significant oxidative stress and toxic i-As accumulation in lettuce leaves. These findings underscore the importance of considering both organic and inorganic arsenic species when assessing arsenic contamination risks in agricultural systems and food safety.