Jeanne E. Tomaszewski

Activated carbon amendment as a treatment for residual DDT in sediment from a superfund site in San Francisco Bay, Richmond, California, USA.

Pesticide formulators formerly operating at Lauritzen Channel, a portion of San Francisco Bay near Richmond (CA, USA), caused contamination of sediment with dichlorodiphenyltrichloroethane (DDT). The present study evaluated the distribution of residual DDT in channel sediment six years following extensive remedial dredging. High DDT concentrations (up to 252 mg/ kg) were found in Young Bay Mud sampled across the channel. Particle analyses showed most of the contamination is contained in the clay/silt sediment fraction, and desorption tests showed that availability is greater for DDT metabolites than parent DDT. The present study examined the feasibility of using activated carbon amendment to sequester DDT from sediment, including an evaluation of reactivated carbon as a less costly alternative to virgin activated carbons. Treatment success of activated carbon amendment to sediment collected from Lauritzen Channel was measured by reductions in aqueous equilibrium concentrations and uptake in semipermeable membrane devices (SPMDs). Four different activated carbons were tested and, after one month of treatment with 3.2 weight % carbon, DDT aqueous equilibrium concentrations were reduced up to 83% and SPMD uptake was reduced up to 91%. Reactivated carbon was comparable with virgin carbons in all tests. Reduction in SPMD uptake of DDT by treatment with 3.2% reactivated carbon increased to 99% after 26 months of treatment. The effectiveness of activated carbon was dependent on the type, size, dose, and contact time. The results show the potential usefulness of activated carbon amendment as a follow-up remedial technology for management of residuals after dredging contaminated sediment.

Sorption of dichlorodiphenyltrichloroethane (DDT) and its metabolites by activated carbon in clean water and sediment slurries.

Polyethylene-water partitioning coefficients (K(PE)) and mass transfer coefficients (k(PE)) for the ortho and para isomers of the organochlorine pesticide dichlorodiphenyltrichloroethane (DDT) and its metabolites dichlorodiphenyldichloroethane (DDD), dichlorodiphenyldichloroethylene (DDE) and, dichlorodiphenylmonochloroethylene (DDMU) were measured. These data were used to derive activated carbon (AC) sorption isotherms in clean water in the sub-nanogram per litre free aqueous concentration range for a virgin and a regenerated AC. The sorption strength of AC for DDT and its metabolites was very high and logarithmic values of the AC-water partitioning coefficients, logK(AC), ranged from 8.47 to 9.26. A numerical mass transfer model was calibrated with this data to interpret previously reported reductions in DDT uptake by semipermeable membrane devices after AC amendment of sediment from Lauritzen Channel, California, USA. The activated carbon-water partitioning coefficient values (K(AC)) measured in clean water systems appear to overestimate the AC sorption capacity in sediment up to a factor 32 for DDT and its metabolites at long contact time with fine-sized AC. Modelling results show decreased attenuation of the AC sorption capacity with increased sediment-AC contact time. We infer that increased resistance in mass transfer of DDTs to sorption sites in the microporous region likely caused by deposits of dissolved organic matter in the macro- and mesopores of AC appears to be the most relevant fouling mechanism. These results suggest that DDTs may diffuse through possible deposits of dissolved organic matter over time, implying that the effects of sediment on the sorption of DDTs by AC may be more kinetic than competitive.

Protein encapsulation by humic substances.

Protein encapsulation by natural organic matter is hypothesized to preserve the activity of proteins in terrestrial and aquatic environments. Direct molecular-level evidence for encapsulation of net positively charged proteins lysozyme, trypsin, and ribonuclease A by a diverse set of humic substances (HS) in nanostructured films was collected using a combination of optical waveguide lightmode spectroscopy and quartz crystal microbalance measurements. The results suggest that protein-HS electrostatic attraction drives encapsulation of positively charged lysozyme by a soil humic acid at pH 5 to 8 and by six additional humic and fulvic acids from terrestrial and mixed terrestrial aquatic sources at pH 5 and 6. Encapsulation of trypsin and ribonuclease A, which had negatively charged surface patches under the studied conditions, suggested that localized protein-HS electrostatic repulsion is overcompensated by attractive forces, likely including contributions from the hydrophobic effect. Evidence is provided showing that encapsulation of lysozyme at pH 8 and of ribonuclease A at pH 5 and 6 involved partial disassembly of HA supramolecular associations. This work advances a molecular-level picture of protein encapsulation by HS and presents a novel approach to study the effects of encapsulation on protein enzymatic activity and susceptibility to abiotic and biotic transformations.

Measuring and modeling reduction of DDT availability to the water column and mussels following activated carbon amendment of contaminated sediment.

A 28-day accumulation study demonstrated the use of mussel uptake, passive samplers, and biodynamic modeling to measure the reduction of dichlorodiphenyltrichloroethane (DDT) availability in the water column after the addition of activated carbon to contaminated sediment. Sediment collected from Lauritzen Channel, Richmond, California (16.5mg total DDT/kg) was mixed with either virgin activated carbon or a reactivated carbon for one month, after which a 28-day laboratory exposure study was completed. Mussels (Mytilus edulis) suspended above activated carbon-treated sediment accumulated significantly less total DDT in soft tissue, 91% and 84% for virgin and reactivated carbon, respectively, as compared to untreated sediment. Mussel tissue concentrations correlated to concentrations in semipermeable membrane devices (SPMDs) and polyethylene devices (PEDs) suspended over the same sediments. A biodynamic model that incorporated DDT water concentrations, either analytically measured or estimated from PED uptake, described mussel accumulation over time. Thus, passive samplers in combination with biodynamic modeling may provide an important screening tool for assessment of filter-feeding uptake and ecological risk to water-dwelling organisms exposed to aqueous phase hydrophobic organic contaminants.

Adsorption of Insecticidal Cry1Ab Protein to Humic Substances. 1. Experimental Approach and Mechanistic Aspects

Adsorption is a key process affecting the fate of insecticidal Cry proteins (Bt toxins), produced by genetically modified Bt crops, in soils. However, the mechanisms of adsorption to soil organic matter (SOM) remain poorly understood. This work assesses the forces driving the adsorption of Cry1Ab to Leonardite humic acid (LHA), used as a model for SOM. We studied the effects of solution pH and ionic strength (I) on adsorption using a quartz crystal microbalance with dissipation monitoring and optical waveguide lightmode spectroscopy. Initial Cry1Ab adsorption rates were close to diffusion-limited and resulted in extensive adsorption, even at pH >6, at which LHA and Cry1Ab carry negative net charges. Adsorption increased with decreasing I at pH >6, indicating Cry1Ab-LHA patch-controlled electrostatic attraction via positively charged domains of Cry1Ab. Upon rinsing, only a fraction of Cry1Ab desorbed, suggesting a range of interaction energies of Cry1Ab with LHA. Different interaction energies likely resulted from nonuniformity in the LHA surface polarity, with higher Cry1Ab affinities to more apolar LHA regions due to the hydrophobic effect. Contributions from the hydrophobic effect were substantiated by comparison of the adsorption of Cry1Ab and the reference proteins albumin and lysozyme to LHA and to apolar and polar model surfaces.

Adsorption of Insecticidal Cry1Ab Protein to Humic Substances. 2. Influence of Humic and Fulvic Acid Charge and Polarity Characteristics

Assessing the fate and potential risks of transgenic Cry proteins in soils requires understanding of Cry protein adsorption to soil particles. The companion paper provided evidence that patch-controlled electrostatic attraction (PCEA) and the hydrophobic effect contributed to Cry1Ab protein adsorption to an apolar humic acid (HA). Here, we further assess the relative importance of these contributions by comparing Cry1Ab adsorption to seven humic substances varying in polarity and charge, at different solution pH and ionic strength, I. Cry1Ab adsorption to relatively apolar HAs at I = 50 mM exhibited rapid initial rates, was extensive, and was only partially reversible at pH 5-8, whereas adsorption to more polar fulvic acids was weak and reversible or absent at pH >6. The decrease in adsorption with increasing HS polarity at all tested pH strongly supports a large contribution from the hydrophobic effect to adsorption, particularly at I = 50 mM when PCEA was effectively screened. Using insect bioassays, we further show that Cry1Ab adsorbed to a selected HA retained full insecticidal activity. Our results highlight the need to consider adsorption to soil organic matter in models that assess the fate of Cry proteins in soils.

Treatment and Containment of Contaminated Sediments

Several approaches to the containment and treatment of contaminated sediment were evaluated, including the efficacy of adding activated carbon to sediment as an in-situ stabilization method and the use of conventional and innovative treatment caps. The applicability of phytoremediation for dredged sediments and sediments in shallow water or wetlands was also explored. The effectiveness of any treatment relies on successful application in the field and the emphasis herein is on evaluation of these approaches in the field. A demonstration at Hunters Point, San Francisco Bay, California strives to prove the efficacy of activated carbon treatment, and stands as an example for applications elsewhere. Simultaneous containment and treatment of sediment contaminants is being demonstrated in the Anacostia River, Washington, DC using both organic and metal sequestering agents incorporated into a cap. Both conventional placement and placement in a laminated mat were demonstrated to provide an array of placement approaches. The laminated mat allowed placement of thin layers of high value material at specific location, enabling the use of high value “active” capping materials such as activated carbon and microscale iron. Phyto- and rhizoremediation using plants and related bacteria is a promising approach for treatment of contaminated sediments, but has its inborn limitations. To overcome the slow performance of the process, transgenic plants were evaluated that express the bacterial gene responsible for cleaving PCBs, or metal binding proteins to provide additional metal binding capacity. Continued development of cap and sediment treatments, and approaches to assess effectiveness and long-term reliability are encouraged.