Evidence is accumulating that sorption of organic chemicals to soils and sediments can be described by "dual-mode sorption": absorption in amorphous organic matter (AOM) and adsorption to carbonaceous materials such as black carbon (BC), coal, and kerogen, collectively termed "carbonaceous geosorbents" (CG). Median BC contents as a fraction of total organic carbon are 9% for sediments (number of sediments, n approximately 300) and 4% for soils (n = 90). Adsorption of organic compounds to CG is nonlinear and generally exceeds absorption in AOM by a factor of 10-100. Sorption to CG is particularly extensive for organic compounds that can attain a more planar molecular configuration. The CG adsorption domain probably consists of surface sites and nanopores. In this review it is shown that nonlinear sorption to CG can completely dominate total sorption at low aqueous concentrations (<10(-6) of maximum solid solubility). Therefore, the presence of CG can explain (i) sorption to soils and sediments being up to 2 orders of magnitude higher than expected on the basis of sorption to AOM only (i.e., "AOM equilibrium partitioning"), (ii) low and variable biota to sediment accumulation factors, and (iii) limited potential for microbial degradation. On the basis of these consequences of sorption to CG, it is advocated that the use of generic organic carbon-water distribution coefficients in the risk assessment of organic compounds is not warranted and that bioremediation endpoints could be evaluated on the basis of freely dissolved concentrations instead of total concentrations in sediment/soil.

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There is an increasing recognition of the necessity to consider the heterogeneity of geosorbents, and in particular the condensed carbon facies fraction, to improve prediction of hydrophobic pollutant phase speciation. Field observations of much elevated organic-carbon normalized distribution coefficients (K oc) of PAHsrelative to predictions from bulk organic-matter partitioning modelshave been suggested to be explainable by soot sorption. To afford testing of this hypothesis, we here report on the soot-water distribution coefficients (K sc) for a series of PAHs (naphthalene (NP), fluorene (FL), phenanthrene (PH), and pyrene (PY)) using diesel particulate matter (NIST standard reference material SRM-1650) as model soot sorbent. Specifically adapted batch and column experiments yielded average log K sc values of 5.23, 5.40, 5.82, and 6.59 (batch) and 4.63, 6.03, 6.62, and 7.03 (column) for NP, FL, PH, and PY, respectively (all data in [Lw/kgsc]). The obtained values are 35−250 times higher than respective K oc predictions and are considerably closer to theoretically estimated soot-water distribution coefficients. Our data are among the highest solid-water distribution coefficients of an environmentally relevant sorbent ever reported and lend direct empirical support of active soot sorption as a viable explanation to the enhanced PAH partitioning. Sorption kinetics on the hours-days time scale and similarity of external geometric and BET surface areas suggest that interaction sites are largely restricted to the outer surface of the soot. The constrained K sc values facilitate prediction of speciation and bioavailable exposures of PAHs in aquatic and sedimentary environments.

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Abstract. Formation of highly condensed black carbon (BC) from vegetation fires and wood fuel combustion presumably transfers otherwise rapidly cycling carbon from the atmosphere-biosphere cycle into a much slower cycling geological form. Recently reported BC fractions of total organic carbon (TOC) in surficial marine sediments span a wide range (2-90%), leaving it presently unclear whether this variation reflects natural processes or is largely due to method differences. In order to elucidate the importance of BC to carbon burial the specificity of applied methods needs to be constrained. Here the operating range and applicability of a commonly used chemothermal oxidation (CTO) method is evaluated using putative BC standards, potentially interfering substances, and natural matrix standards. Test results confirm the applicability of the method to marine sediments. Integrity tests with model substrates suggest applicability to low-carbon soils but only with a lower specificity to seawater particulate matter. The BC content of marine sediment samples in a set of studies employing the CTO method proved to be consistent with associated geochemical information. The radiocarbon content of the BC isolate in an environmental matrix standard was shown to be similar to the radiocarbon signature of pyrogenic polycyclic aromatic hydrocarbons (PAHs), here serving as molecular markers of combustion (fraction modemfM of BC was 0.065 + 0.014 and of PAHs 0.056 + 0.020), while being clearly distinct from the radiocarbon content of the bulk TOC (fM= 0.61 + 0.08). Urgent questions such as the global accumulation rate of black carbon in soils and sediments may prove approachable with the chemothermal oxidation technique of BC quantification.

Scientific publications and patents on nanomaterials (NM) used in plant protection or fertilizer products have exponentially increased since the millennium shift. While the United States and Germany have published the highest number of patents, Asian countries released most scientific articles. About 40% of all contributions deal with carbon-based NM, followed by titanium dioxide, silver, silica, and alumina. Nanomaterials come in many diverse forms (surprisingly often ≫100 nm), from solid doped particles to (often nonpersistent) polymer and oil-water based structures. Nanomaterials serve equally as additives (mostly for controlled release) and active constituents. Product efficiencies possibly increased by NM should be balanced against enhanced environmental NM input fluxes. The dynamic development in research and its considerable public perception are in contrast with the currently still very small number of NM-containing products on the market. Nanorisk assessment and legislation are largely in their infancies.

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