Native Oxy-PAHs, N‑PACs, and PAHs in Historically Contaminated Soils from Sweden, Belgium, and France: Their Soil-Porewater Partitioning Behavior, Bioaccumulation in <i>Enchytraeus crypticus</i>, and Bioavailability

Soil quality standards are based on partitioning and toxicity data for laboratory-spiked reference soils, instead of real world, historically contaminated soils, which would be more representative. Here 21 diverse historically contaminated soils from Sweden, Belgium, and France were obtained, and the soil-porewater partitioning along with the bioaccumulation in exposed worms (<i>Enchytraeus crypticus</i>) of <i>native</i> polycyclic aromatic compounds (PACs) were quantified. The native PACs investigated were polycyclic aromatic hydrocarbons (PAHs) and, for the first time to be included in such a study, oxygenated-PAHs (oxy-PAHs) and nitrogen containing heterocyclic PACs (N-PACs). The passive sampler polyoxymethylene (POM) was used to measure the equilibrium freely dissolved porewater concentration, <i>C</i>_pw, of all PACs. The obtained organic carbon normalized partitioning coefficients, <i>K</i>_TOC, show that sorption of these native PACs is much stronger than observed in laboratory-spiked soils (typically by factors 10 to 100), which has been reported previously for PAHs but here for the first time for oxy-PAHs and N-PACs. A recently developed <i>K</i>_TOC model for historically contaminated sediments predicted the 597 unique, native <i>K</i>_TOC values in this study within a factor 30 for 100% of the data and a factor 3 for 58% of the data, <i>without</i> calibration. This model assumes that TOC in pyrogenic-impacted areas sorbs similarly to coal tar, rather than octanol as typically assumed. Black carbon (BC) inclusive partitioning models exhibited substantially poorer performance. Regarding bioaccumulation, <i>C</i>_pw combined with liposome-water partition coefficients corresponded better with measured worm lipid concentrations, <i>C</i>_lipid (within a factor 10 for 85% of all PACs and soils), than <i>C</i>_pw combined with octanol–water partition coefficients (within a factor 10 for 76% of all PACs and soils). <i>E. crypticus</i> mortality and reproducibility were also quantified. No enhanced mortality was observed in the 21 historically contaminated soils despite expectations from PAH spiked reference soils. Worm reproducibility weakly correlated to <i>C</i>_lipid of PACs, though the contributing influence of metal concentrations and soil texture could not be taken into account. The good agreement of POM-derived <i>C</i>_pw with independent soil and lipid partitioning models further supports that soil risk assessments would improve by accounting for bioavailability. Strategies for including bioavailability in soil risk assessment are presented

Chromium(III) Complexation to Natural Organic Matter: Mechanisms and Modeling

Chromium is a common soil contaminant, and it often exists as chromium­(III). However, limited information exists on the coordination chemistry and stability of chromium­(III) complexes with natural organic matter (NOM). Here, the complexation of chromium­(III) to mor layer material and to Suwannee River Fulvic Acid (SRFA) was investigated using EXAFS spectroscopy and batch experiments. The EXAFS results showed a predominance of monomeric chromium­(III)-NOM complexes at low pH (<5), in which only Cr···C and Cr–O–C interactions were observed in the second coordination shell. At pH > 5 there were polynuclear chromium­(III)-NOM complexes with Cr···Cr interactions at 2.98 Å and for SRFA also at 3.57 Å, indicating the presence of dimers (soil) and tetramers (SRFA). The complexation of chromium­(III) to NOM was intermediate between that of iron­(III) and aluminum­(III). Chromium­(III) complexation was slow at pH < 4: three months or longer were required to reach equilibrium. The results were used to constrain chromium-NOM complexation in the Stockholm Humic Model (SHM): a monomeric complex dominated at pH < 5, whereas a dimeric complex dominated at higher pH. The optimized constant for the monomeric chromium­(III) complex was in between those of the iron­(III) and aluminum­(III) NOM complexes. Our study suggests that chromium­(III)-NOM complexes are important for chromium speciation in many environments