Human exposure to bisphenol A (BPA) can occur in contaminated rivers where levels range from 5 to 1500 ng/L. River sediment levels can range from 5 to 100 µg/kg of sediment. BPA MW 228, Melting Pt. 150 C, log P=4.04, pKa 9.5, water solubility =125 mg/L at 25 C. Compare the range of BPA concentrations in river water and sediment after converting both unit ranges to pp. Why is there this difference in level between water and sediment?