Industrially synthesized single-walled carbon nanotubes: compositional data for users, environmental risk assessments, and source apportionment.

Commercially available single-walled carbon nanotubes (SWCNTs) contain large percentages of metal and carbonaceous impurities. These fractions influence the SWCNT physical properties and performance, yet their chemical compositions are not well defined. This lack of information also precludes accurate environmental risk assessments for specific SWCNT stocks, which emerging local legislation requires of nanomaterial manufacturers. To address these needs, we measured the elemental, molecular, and stable carbon isotope compositions of commercially available SWCNTs. As expected, catalytic metals occurred at per cent levels (1.3-29%), but purified materials also contained unexpected metals (e.g., Cu, Pb at 0.1-0.3 ppt). Nitrogen contents (up to 0.48%) were typically greater in arc-produced SWCNTs than in those derived from chemical vapor deposition. Toluene-extractable materials contributed less than 5% of the total mass of the SWCNTs. Internal standard losses during dichloromethane extractions suggested that metals are available for reductive dehalogenation reactions, ultimately resulting in the degradation of aromatic internal standards. The carbon isotope content of the extracted material suggested that SWCNTs acquired much of their carbonaceous contamination from their storage environment. Some of the SWCNTs, themselves, were highly depleted in (13)C relative to petroleum-derived chemicals. The distinct carbon isotopic signatures and unique metal 'fingerprints' may be useful as environmental tracers allowing assessment of SWCNT sources to the environment.

Importance of black carbon to sorption of native PAHs, PCBs, and PCDDs in Boston and New York harbor sediments.

The solid-water distribution ratios (Kd values) of "native" PAHs, PCBs, and PCDDs in Boston and New York Harbor sediments were determined using small passive polyethylene samplers incubated for extended times in sediment-water suspensions. Observed solid-water distribution coefficients exceeded the corresponding f(oc)Koc products by 1-2 orders of magnitude. It was hypothesized that black carbon (fBC), measured in the Boston harbor sediment at about 0.6% and in the New York harbor sediment at about 0.3%, was responsible for the additional sorption. The overall partitioning was then attributed to absorption into the organic carbon and to adsorption onto the black carbon via Kd = f(oc)Koc + f(BC)K(BC)C(w)n-1 with Cw in microg/L. Predictions based on published Koc, K(BC), and n values for phenanthrene and pyrene showed good agreement with observed Kd,obs values. Thus, assuming this dual sorption model applied to the other native PAHs, PCBs, and PCDDs, black carbon-normalized adsorption coefficients, K(BC)S, were deduced forthese contaminants. Log K(BC) values correlated with sorbate hydrophobicity for PAHs in Boston harbor (log K(BC) approximately 0.83 log gamma w(sat) - 1.6; R2 = 0.99, N= 8). The inferred sorption to the sedimentary BC phase dominated the solid-water partitioning of these compound classes, and its inclusion in these sediments is necessary to make accurate estimates of the mobility and bioavailability of PAHs, PCBs, and PCDDs.

Colloid mobilization in the field using citrate to remediate chromium.

We investigated the feasibility of cleaning aquifer sediments, long contaminated with chromium (Cr) from a metal plating facility, by detaching colloid-sized sorbents from the immobile aquifer solids and then pumping those colloids to the surface for treatment. In laboratory experiments using aquifer solids from the site, several solutions (water at various pHs, phosphate, oxalate, ascorbate, citrate) were examined for their ability to disperse colloids and Cr. Based on these tests, a 5 mM citrate solution at pH 7 was selected. Subsequently, such a citrate solution was used in the field in two single-well injection-withdrawal experiments. Large quantities of colloids were released immediately after injection. The colloidal particles mobilized by citrate in the field had more than 20 times higher Cr concentrations than did the average aquifer sediments, implying success in mobilizing Cr-associated phases. Further, laboratory and field tests showed that anion exchange of citrate for chromate caused some additional release of Cr from these aquifer solids.

Fate of linear alkylbenzenes released to the coastal environment near Boston Harbor.

Linear alkylbenzenes (LABs) were used to assess the fates of hydrophobic organic compounds (HOCs) released to a large urban harbor and the adjoining offshore waters. We found that particulate concentrations of the individual C12 LAB isomers in 1996 summertime surface waters decreased from 1 pM in Boston Harbor to 20-200 fM in coastal Massachusetts and Cape Cod Bays. Levels fell to only a few fM in offshore Gulf of Maine locations. These observations were consistent with municipal wastewater in Boston Harbor as the predominant input followed by dispersal via known circulation patterns in this region. Phase-dependent removal rate coefficients for flushing, vertical scavenging, volatilization, photodegradation, and biodegradation of individual LAB isomers were constrained from literature, field observations, and laboratory experiments and combined with estimates of wastewater release rates into a predictive 3-box model. Vertical scavenging, biodegradation, and flushing were predicted to be the most important fate processes for C12 LABs in the Boston Harbor-MA Bay-Cape Cod Bay flow system with about 1% of the harbor releases "surviving" passage. For HOCs such as the relatively bio-recalcitrant LAB, 6-phenyldodecane, it appears that we are at present able to predict the coastal fate of harbor-introduced HOCs in this system within a factor of 2. Contrary to expectations from biodegradation experiments, the ratio of internal-to-external (I/E) LAB isomers decreased offshore in both water and sediment samples, suggesting we are "missing" an important process affecting LAB fates.

Enhanced concentrations of PAHs in groundwater at a coal tar site.

Concentrations of polycyclic aromatic hydrocarbons (PAHs) in groundwater at a coal tar site were elevated by factors ranging from 3 (pyrene) to 50 (indeno[1,2,3-cd]pyrene) over purely dissolved concentrations. Air-groundwater surface tension measurements (70.6 +/- 3 dyn/cm) were not sufficiently different from air-pure water measures (72.2 +/- 0.1 dyn/cm) to ascribe the observed enrichments to either cosolvents or surfactants in the groundwater. Excess pyrene was associated with colloids that passed an ultrafilter at ambient pH but became ultrafilterable when the groundwater pH was lowered to 1. This suggested pyrene association with humic acids. Given the decrease in groundwater total organic carbon (TOC) of 4 mgc/L upon acidification and ultrafiltration, a partition coefficient of 10(5) L/kgc was estimated for this pyrene association. Use of the results for pyrene and scaling for the differences in PAH hydrophobicities enabled good predictions of the observed enrichments of less water-soluble PAHs in the groundwater. This is strong field evidence indicating colloid-facilitated transport of HOCs in groundwater. Assuming that humic-bound PAHs were as mobile as the dissolved PAHs, the fluxes of individual PAHs (e.g., benzo[a]pyrene) from the tar source were as much as 20 times greater than estimates based solely on tarwater partitioning predictions.

By-products of a former phenol manufacturing site in a small lake adjacent to a Superfund site in the Aberjona watershed.

Benzene, diphenyl sulfone (DPS), para-hydroxybiphenyl (PPP), ortho-hydroxybiphenyl (OPP), higher hydroxybiphenyls, and alkylated benzenes were found in a small lake receiving contaminated groundwater discharge from the Industri-Plex Superfund site (Woburn, MA) in the Aberjona watershed in eastern Massachusetts. All of these chemicals may derive from the former phenol manufacturing activities present at the Industri-Plex site during World War I. Concentrations up to 1660 microgram/l benzene, 450 micro/l DPS, 230 microgram/l PPP, and 100 microgram/l OPP were detected in the hypolimnion. Epilimnetic concentrations of the chemicals were significantly lower (normally < 5 microgram/l). DPS showed a distinct seasonal behavior: It was readily biodegradable during warm periods. No biodegradation was observed in the winter, leaving export to the Aberjona River as the major removal mechanism. Although benzene is known to be toxic and a human carcinogen, our results indicate that DPS, OPP, and PPP are not mutagenic in tests using human MCL-5 and h1A1v2 cell lines.

Volatile halogenated organic compounds released to seawater from temperate marine macroalgae.

Volatile halogenated organic compounds synthesized by various industrial processes are troublesome pollutants because they are persistent in terrestrial ecosystems and because they may be present in sufficient quantities to alter the natural atmospheric cycles of the halogens. Certain of these compounds, including polybromomethanes and several previously unobserved alkyl monohalides and dihalides, appear to be natural products of the marine environment. A variety of temperate marine macroalgae (the brown algae Ascophyllum nodosum and Fucus vesiculosis, the green algae Enteromorpha linza and Ulva lacta, and the red alga Gigartina stellata) not only contain volatile halogenated organic compounds but also release them to seawater at rates of nanograms to micrograms of each compound per gram of dry algae per day. The macroalgae may be an important source of bromine-containing material released to the atmosphere.