Use of Autometallography to Localize and Semi-Quantify Silver in Cetacean Tissues

Silver nanoparticles (AgNPs) have been extensively used in commercial products, including textiles, cosmetics, and health care items, due to their strong antimicrobial effects. They also may be released into the environment and accumulate in the ocean. Therefore, AgNPs are the major source of Ag contamination, and public awareness of the environmental toxicity of Ag is increasing. Previous studies have demonstrated the bioaccumulation (in producers) and magnification (in consumers/predators) of Ag. Cetaceans, as the apex predators of ocean, may have been negatively affected by the Ag/Ag compounds. Although the concentrations of Ag/Ag compounds in cetacean tissues can be measured by inductively coupled plasma mass spectroscopy (ICP-MS), the use of ICP-MS is limited by its high capital cost and the requirement for tissue storage/preparation. Therefore, an autometallography (AMG) method with an image quantitative analysis by using formalin-fixed, paraffin-embedded (FFPE) tissue may be an adjuvant method to localize Ag distribution at the suborgan level and estimate the Ag concentration in cetacean tissues. The AMG positive signals are mainly brown to black granules of various sizes in the cytoplasm of proximal renal tubular epithelium, hepatocytes, and Kupffer cells. Occasionally, some amorphous golden yellow to brown AMG positive signals are noted in the lumen and basement membrane of some proximal renal tubules. The assay for estimating the Ag concentration is named the Cetacean Histological Ag Assay (CHAA), which is a regression model established by the data from image quantitative analysis of the AMG method and ICP-MS. The use of AMG with CHAA to localize and semi-quantify heavy metals provides a convenient methodology for spatio-temporal and cross-species studies.