Metal(loid) accumulation and foliar physiological responses in Oryza sativa L. induced by PM1 exposure from various emission sources

Foliar uptake of airborne metal(loid)s plays a crucial role in metal(loid) accumulation in plant organs and is influenced by the size and emission sources of aerosols. Given the high enrichment of toxic metal(loid)s in submicron-scale particulates (PM₁), this study established a PM₁ exposure system to examine airborne metal(loid) accumulation and foliar physiological responses in Oryza sativa L. The results showed that the concentrations of Cu, Zn, As, Pb, and Cd in the leaves and grains were influenced not only by the airborne metal(loid) levels but also by the specific nature of the PM₁ particles. The quantitative model for PM₁-associated Pb entry into leaf tissue indicated that foliar Pb accumulation was primarily driven by particle adhesion, followed by hydrophilic penetration and trans-stomatal liquid film migration, accounting for 87 %-89 % of the total accumulation. The strong hygroscopicity and high Pb activity of PM₁ emitted from waste incineration (WI) increased the Pb absorption coefficient via the hydrophilic and liquid film migration pathway. In contrast, the high hydrophobicity of PM₁ from coal burning (CB) led to greater retention of Pb on leaf surfaces. Both foliar reactive oxygen metabolism and photosynthesis indices were sensitive to air pollution. Foliar metal(loid) accumulation and airborne PM₁ concentration accounted for the variance in physiological responses in rice leaves. Our results also indicated that Pb was the key element in PM₁ emissions from both coal burning (CB) and waste incineration (WI) responsible for significant physiological changes in rice leaves.