Characterization of PM₁₀-bound metal speciation, bioavailability, and plant responses in Andrographis paniculata at a...

Understanding the intricate fate of atmospheric particulate matter (PM₁₀)-associated heavy metals within medicinal plants is crucial for environmental and public health. This study rigorously investigated the speciation, bioavailability, and cellular-physiological impacts of PM₁₀-borne lead (Pb), cadmium (Cd), and arsenic (As) on Andrographis paniculata, tracing their dynamics across soil and plant tissues. The experiment was conducted near a busy traffic junction, comparing uncontaminated (T1) and metal-contaminated (T2) soils. PM₁₀-Pb was predominantly (76%) in the residual fraction, whereas Cd was largely (66.5%) in the oxidizable fraction. As concentrations were too low for detailed PM₁₀ fractionation. In A. paniculata, Pb exhibited higher accumulation but lower mobility than Cd. PM deposition induced significant leaf surface roughening, aggregate formation at trichomes, and altered stomatal morphology. The multivariate analysis delineated the dynamic relationship between PM₁₀-associated metal speciation and their subsequent subcellular sequestration. Also, the distinct metal sequestration profiles between T1 and T2 treatments were discriminated. Analysis results indicated direct interaction of water-soluble PM₁₀ metal forms with cellular components. In contrast, oxidizable and residual forms demonstrated intracellular biotransformation into more bioavailable states. In T1, a higher proportion of bioavailable metal forms (EtOH and H₂O-extractable) was observed, correlating with enhanced organelle accumulation, indicative of a comparatively less robust detoxification capacity. Conversely, T2 shifted to less bioavailable forms (HAc, HCl, and NaCl extractable), reducing organelle uptake. While antioxidant enzyme activity increased in both, growth and andrographolide content decreased. This research provides novel insights into plant adaptive strategies against atmospheric metal stress under varying soil conditions.