Effect of dissolved organic matter from Canadian shield lakes on the bioavailability of 1,3,6,8‐Tetrachlorodibenzo‐p‐dioxin to the amphipod Crangonyx laurentianus

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Abstract
The effect of dissolved organic matter (DOM) on the apparent solubility and bioavailability of 1,3,6,8‐tetrachlorodibenzo‐p‐dioxin (1,3,6,8‐TCDD) was examined in epilimnetic and sediment interstitial waters collected from the Canadian Shield lakes in the Experimental Lakes Area of Northwestern Ontario. DOM enhanced the apparent solubility of 1,3,6,8‐TCDD by as much as three times over the reference DOM‐free water (DOM Crangonyx laurentianus decreased in the presence of DOM. Only the 1,3,6,8‐TCDD that was truly in solution was apparently available for uptake by biota. The quality or site of collection of the DOM was also an important factor. Sediment interstitial waters had a greater affinity for 1,3,6,8‐TCDD than did epilimnetic waters, as indicated by the DOC partition coefficients. Although the DOM may enhance the apparent solubility of 1,3,6,8‐TCDD, DOM also reduces the amount of 1,3,6,8‐TCDD truly free in solution and therefore bioavailable. Solubility enhancement may, however, lead to greater dispersion of 1,3,6,8‐TCDD and low‐level exposure of biota as the 1,3,6,8‐TCDD gradually desorbs from the TCDD‐DOM complex.

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