2 research outputs found
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><sub>pw</sub>, of all PACs. The obtained organic carbon normalized partitioning
coefficients, <i>K</i><sub>TOC</sub>, 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><sub>TOC</sub> model for historically
contaminated sediments predicted the 597 unique, native <i>K</i><sub>TOC</sub> 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><sub>pw</sub> combined with liposome-water partition coefficients corresponded
better with measured worm lipid concentrations, <i>C</i><sub>lipid</sub> (within a factor 10 for 85% of all PACs and soils),
than <i>C</i><sub>pw</sub> 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><sub>lipid</sub> 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><sub>pw</sub> 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 chromiumÂ(III).
However, limited information exists on the coordination chemistry
and stability of chromiumÂ(III) complexes with natural organic matter
(NOM). Here, the complexation of chromiumÂ(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 chromiumÂ(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
chromiumÂ(III)-NOM complexes with Cr···Cr interactions
at 2.98 Ã… and for SRFA also at 3.57 Ã…, indicating the presence
of dimers (soil) and tetramers (SRFA). The complexation of chromiumÂ(III)
to NOM was intermediate between that of ironÂ(III) and aluminumÂ(III).
ChromiumÂ(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 chromiumÂ(III)
complex was in between those of the ironÂ(III) and aluminumÂ(III) NOM
complexes. Our study suggests that chromiumÂ(III)-NOM complexes are
important for chromium speciation in many environments