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In the present study, the reduced adsorption of propanil on black carbon (BC) influenced by dissolved organic matter (DOM) was verified to be closely related to DOM molecule size and loading mode. Two congenetic carbons, a rice-residue-derived BC and the reduced product (RC), were characterized by similar specific surface area and different surface properties. Reduced product exhibits higher adsorption of propanil and DOM than BC. A series of model DOMs, including tannic acid (TA), pentagalloylglucose (PA), 3-O-galloylmucic acid (OA), and gallic acid (GA), characterized by different molecule sizes and molecular weights, were used to evaluate the different inhibitory effects. The DOM adsorption (mmol/g) on BC and RC follows the order of GA > PA > OA > TA, whereas the reduction of propanil adsorption influenced by the model DOM follows the order of PA ≈ TA > OA ≈ GA. The suppressive degree is connected to their molecule sizes rather than to molecular weights. Tannic acid and PA weakened propanil adsorption more effectively than OA and GA because the large DOM molecules may hinder propanil molecules into the micropore regions. Because of the similar molecule size, TA and PA present a similar suppressive effect on propanil adsorption. The influence of the DOMs was greater when preloaded than when in competition with propanil. The preloading of macromolecules (TA and PA) and OA on the carbons may lead to secondary and primary micropore blocks, respectively. The preloading of GA may cause partial GA molecule sequestration in the primary micropore, thus leading to strong attenuation of propanil adsorption on the carbons. Environ. Toxicol. Chem. 2012;31:1187-1193. © 2012 SETAC [ABSTRACT FROM AUTHOR]

A poor understanding of tributyltin (TBT) sorption on sediments has hindered an accurate evaluation of its environmental fate. The present study determined TBT sorption by a freshwater sediment (BH) and a coastal marine sediment (TZ) as influenced by pH, salinity, and biochar (BC) amendment into TZ. The isotherms were essentially linear, with KOC values in the range of 104 to 105 L/kg. Tributyltin sorption at pH 3.56 and 8.00 occurred mainly via partitioning. It reached maxima at pH equal to its p Ka (=6.25) because of added ion exchange. A salinity increase from 5 to 35 practical salinity units enhanced TBT sorption at pH 3.56 and 8.00 on TZ by approximately 30% and on BH by approximately 80%, ascribed to the salting-out effect that reduced the solubilities of tributyltin hydroxide (TBTOH) and tributyltin chloride (TBTCl). At pH 6.25, the same salinity increase reduced TBT sorption on TZ by approximately 20% but enhanced TBT sorption on BH by approximately 35%. This was attributed to the enhancing role of salting out and the reducing role of metal competition for ion exchange. Tributyltin was two orders of magnitude more effectively sorbed by BC than by total organic carbon of TZ, mainly because of the high level of surface area of the BC. Although BC affinity for TBT may be significantly diminished when present in TZ, it was considered to be the primary contributor to TBT sorption from water. Biochar may thus be used to immobilize TBT in sediment for potential remediation. Environ. Toxicol. Chem. 2011;30:2682-2687. © 2011 SETAC [ABSTRACT FROM AUTHOR]