Preferential accumulation of PM₁-associated metals in Sprague-Dawley rats’ tissues/organs as a consequence of intravenous administration of Delhi’s airborne PM₁

Abstract

Airborne particulate matter (PM) encompasses particles of different sizes with numerous chemical species. Toxicological and epidemiological studies have indicated that the toxicity of PM is primarily due to adsorbed toxic metals. Upon entering the systemic circulation, these PM-bound metals accumulate in multiple organs and induce adverse health effects. Using a murine model, this study examines the organ-specific fate of real-world submicron aerosol (PM₁, aerodynamic diameter ≤ 1 μm). PM₁ samples were collected continuously for 24 h between November 22, 2018 and June 30, 2019, from an industrial cum residential location, i.e., Okhla Industrial Area-I, New Delhi (28.52°N,77.27°E). Samples were extracted and prepared for metal analysis and intravenous (IV) injection. Sprague-Dawley male rats (n = 18) were sourced and stratified into three equal groups: control (saline), low-dose (80.5 µg/kg) and high-dose (244.6 µg/kg). The rats of two groups (low and high) were exposed to PM₁ intravenously, not via inhalation, on a weekly basis for 70 days. Whereas, the control group was exposed to saline via the same route. Upon completion of the PM₁ exposure, rats were euthanised, and their lungs, hearts, kidneys, spleen, liver, cerebrum, cerebellum, and blood were harvested. The tissue samples from these organs were analysed using inductively coupled plasma optical emission spectroscopy (ICP-OES) to quantify metal concentrations in the organs and blood. For multiple-group comparisons, one-way ANOVA was performed (p < 0.05), followed by Tukey’s post hoc test. The metals are ranked based on their preferential accumulation in the different tissues/organs of the rats from the highest to the lowest concentration, as Al, Fe, Ni, Cr, Cu, Pb, Mn, Mo, Zn, Co, Cd, and V. Al was highly accumulated in the kidneys, spleen, and cerebellum, while significant Fe accumulation was observed in the liver, spleen, heart, and cerebellum. Furthermore, substantial accumulation of Pb was witnessed in the bloodstream and vital organs, specifically the lungs, heart, kidneys, liver, and brain, indicating its high mobility and widespread systemic dissemination. Cr was significantly accumulated in the blood, kidneys, heart, cerebrum, and cerebellum, while Cu was in the blood, lungs and heart. Distinct organ-specific targeting was also observed, with Co, Ni and Zn localised primarily in the spleen, heart, and kidneys, respectively. V was found high in the lungs, kidneys, and heart. Conversely, Cd and other toxic trace metals showed no significant organ-level accumulation, suggesting constrained bioavailability, limited cellular uptake, or distinct metabolic clearance pathways under given PM₁ exposure conditions. However, a key limitation of this study is that the IV model does not fully replicate the physiological mechanism of real-world inhalation exposure.

Graphical abstract