TEM of TNP taken up by C57BL/6 alveolar macrophages 1.5 h in vitro post-exposure (25 μg/mL). A) No particle control AM. B) TNB-exposed AM. Arrow indicates abnormal phagolysosomal enlargement. C) High magnification of enlarged phagolysosome in TNB-exposed AM. D) Humic acid-modified TNB-exposed AM. E) Carboxylated TNB-exposed AM. F) High magnification of carboxylated TNB-exposed AM. Black spotted/speckled areas indicate areas of particle retention in the cytoplasm of the macrophage cells.