2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a toxic and persistent organic pollutant found in soils and sediments. It has been linked to several adverse health outcomes in humans and wildlife, including suppression of the immune system. TCDD is strongly sorbed to soils/sediments due to its extremely low water solubility. Presently, the bioavailability of soil/sediment-sorbed TCDD to mammals is not completely understood. Our previous studies demonstrated that TCDD adsorbed to representative inorganic geosorbents (i.e. porous silica and smectite clay) exhibited the same bioavailability to mice as TCDD dissolved in corn oil, whereas sequestration by activated carbons eliminated TCDD bioavailability. In this study, we evaluated the effects of amorphous natural organic matter (NOM), primarily in the form of aquatic humic and fulvic acids, on the mouse bioavailability of TCDD. An aqueous suspension of TCDD mixed with NOM was administered to mice via oral gavage. The relative bioavailability of TCDD was assessed by two sensitive aryl hydrocarbon receptor-mediated responses in mice: 1) hepatic induction of cyp1A1 mRNA; and 2) suppression of immunoglobulin M (IgM) antibody-forming cell (AFC) response which is an indicator of immunotoxicity. Hepatic induction of cyp1A1 mRNA and suppression of IgM AFC induced by TCDD were similar in the NOM-sorbed form and dissolved in corn oil, revealing no loss of bioavailability when associated with NOM. Hence, NOM-associated TCDD is as capable of suppressing humoral immunity in mice as TCDD dissolved in corn oil, indicating that NOM-sorbed TCDD is likely to fully retain its bioavailability to mammals and, by inference, humans.

2,3,7,8-四氯二苯并-对-二恶英 (TCDD) 是一种存在于土壤和沉积物中的有毒和持久性有机污染物。它与人类和野生动物的多种不良健康结果有关，包括抑制免疫系统。由于其极低的水溶性，TCDD 会被土壤/沉积物强烈吸附。目前，土壤/沉积物吸附的 TCDD 对哺乳动物的生物利用度尚不完全清楚。我们之前的研究表明，吸附到代表性无机地质吸附剂（即多孔二氧化硅和蒙脱石粘土）上的 TCDD 对小鼠表现出与溶解在玉米油中的 TCDD 相同的生物利用度，而活性炭螯合消除了 TCDD 的生物利用度。在这项研究中，我们评估了无定形天然有机物 (NOM) 的影响，主要以水生腐殖酸和富里酸的形式存在，小鼠 TCDD 的生物利用度。通过口服强饲法将 TCDD 与 NOM 混合的水性悬浮液施用于小鼠。TCDD 的相对生物利用度通过小鼠中两种敏感的芳基烃受体介导的反应进行评估：1) cyp1A1 mRNA 的肝诱导；2) 免疫球蛋白 M (IgM) 抗体形成细胞 (AFC) 反应的抑制，这是免疫毒性的一个指标。肝脏诱导cyp1A1 mRNA 和 TCDD 诱导的 IgM AFC 抑制在 NOM 吸附形式和溶解在玉米油中相似，表明与 NOM 相关时生物利用度没有损失。因此，与 NOM 相关的 TCDD 与溶解在玉米油中的 TCDD 一样能够抑制小鼠的体液免疫，这表明 NOM 吸附的 TCDD 可能会完全保留其对哺乳动物的生物利用度，并据此推论人类。