The physical and kinetic speciation of Cu and Zn in three impacted marine estuaries was examined. Contrasts in sources of metal-binding ligands, solution chemistry, and hydrologic forcing between and withinthethree study systems (Cape Fear River Estuary, North Carolina; Norfolk-Hampton Roads-Elizabeth River, Virginia; San Diego Bay, California) were exploited to enhance our understanding of Cu and Zn speciation. Trace metal-optimized tangential-flow ultrafiltration at 1 kDa nominal molecular weight limit (NMWL) was used to fractionate <0.4 microm species into colloidal and "dissolved" pools. Colloidal species of dissolved organic matter (DOM) and copper were significant and often the dominant pools in each of the three study systems. Characteristic colloidal fractions of both DOM and Cu ranged from near 70% of <0.4 microm concentrations in Cape Fear to 50% in San Diego Bay. Colloidal Cu and DOM were strongly coupled, and variability in observed <0.4 microm Cu concentrations was closely related to the concentrations of colloidal-associated metal. Colloidal fractions were much smaller for Zn than that of Cu; ranging from 10-30% in Cape Fear to less than 5% in San Diego Bay, and no relationship to DOM was observed. Kinetic separations on Chelex resin revealed the presence of large nonlabile pools of Cu in each of the study systems, with the highest fractions (70-100%) in Cape Fear and Norfolk and lowest (30-50%) in San Diego Bay. A close relationship was observed between colloidal and nonlabile Cu species, implying slow reactivity of colloidal-bound Cu. The fraction of filterable Zn labile to Chelex averaged 97%, 85%, and 60% in San Diego, Norfolk, and Cape Fear, respectively. Anthropogenic Zn appeared almost exclusively in the <1 kDa fraction, while anthropogenic Cu was distributed between dissolved and colloidal pools. Copper particle-partition coefficients (Kd) followed the trend: San Diego >> Norfolk > Cape Fear and were inversely correlated with DOC concentrations. Colloid-based partition coefficients were significantly greater, in many cases an order of magnitude greater, than particle-based partition coefficients. The partitioning data suggest the presence of metal-enriched bacterial-derived exudates and/or discrete metal phases in colloidal-sized particles in impacted regions of these estuaries. The strong relationships observed between Cu and DOC indicate that Cu partitioning behavior over a range of estuarine environments may be modeled effectively with a limited set of coefficients. Our measurements of metal lability and size distribution imply that the fraction of <0.4 microm Zn that is likely to be bioavailable is greater than that for Cu, especially in impacted regions of the study systems.

Using tangential flow ultrafiltration, total mercury (HgT) and methylmercury (MeHg) concentrations in the colloidal phase (0.4 microm-10 kDa) were determined for 15 freshwaters located in the upper Midwest (Minnesota, Michigan, and Wisconsin) and the Southern United States (Georgia and Florida). Unfiltered concentrations were typical of those reported for freshwater and ranged from 0.9 to 27.1 ng L(-1) HgT and from 0.08 to 0.86 ng L(-1) MeHg. For some rivers, HgT and MeHg in the colloidal phase comprised up to 72% of the respective unfiltered concentration. On average, however, HgT and MeHg concentrations were evenly distributed between the particulate (>0.4 microm), colloidal, and dissolved (<10 kDa) phases. The pool of Hg in the colloidal phase decreased with increasing specific conductance. Results from experiments on freshwaters with artificially elevated specific conductance suggest that HgT and MeHg may partition to different subfractions of colloidal material. The colloidal-phase HgT correlation with filtered organic carbon (OC(F)) was generally poor (r2 < 0.14; p > 0.07), but the regression of MeHg with OC(F) was strong, especially in the upper Midwest (r2 = 0.78; p < 0.01). On a mass basis, colloidal-phase Hg concentrations were similar to those of unimpacted sediments in the Midwest. Mercury to carbon ratios averaged 352 pg of HgT/mg of C and 25 pg of MeHg/mg of C and were not correlated to ionic strength. The log of the partition coefficient (log K(D)) for HgT and MeHg ranged from 3.7 to 6.4 and was typical of freshwater values determined using a 0.4 microm cutoff between the particulate phase and the dissolved phase. Log K(D) calculated using the <10 kDa fraction as "dissolved" ranged from 4.3 to 6.6 and had a smaller standard deviation about the mean. In addition, our data support the "particle concentration effect" (PCE) hypothesis that the association of Hg with colloids in the filter-passing fraction can lower the observed log K(D). The similarity between colloidal and particulate-phase partition coefficients suggests that colloidal mass and not preferential colloidal partitioning drives the PCE.

Laboratory and field investigations of 10 kDa polyethersulfone (PES) and regenerated cellulose (RCL) membranes were conducted to evaluate the utility of ultrafiltration (UF) for low-level mercury determinations in freshwaters. Laboratory investigations focused on blank levels, sorption loss, and charge rejection; while field investigations addressed mass balance closure, replicate precision, and permeate trends in concentration. A thorough mass balance approach was used throughout the investigation, and experiments were conducted across typical gradients in freshwater pH, specific conductance, and dissolved organic carbon (DOC). The minim um source-water Hg-T concentration that could be confidently processed from a 5 L volume was 0.5 ng L-1 for PES and 1.4 ng L-1 for RCL as determined by three times the standard deviation of our method blank. The minimum source-water MeHg concentration was 0.5 ng L-1 for PES and 0.2 ng L-1 for RCL based on river-water mass balance results. Mass balance closures were generally better for RCL than PES, especially for MeHg where 95% of the residuals (n = 21) were within +/-30% of closure. Duplicate UF separations on RCL membranes, and between RCL and PES membranes, agreed within 16% in the colloidal and dissolved fractions for both total mercury (Hg-T) and MeHg. Mercury sorption loss and charge rejection were greater for PES membranes than RCL membranes, especially for low ionic strength waters (<100 mu S cm(-1)). Increases in permeate concentration were observed as the UF separation progressed, and preconditioning the membrane with a subsample of the feed solution did not substantially improve the performance. Overall, RCL outperformed PES membranes in low ionic strength waters and therefore is preferred for investigations of mercury partitioning under ambient freshwater conditions.

QUANTITATIVE ANALYSIS OF THE DETECTION LIMITS FOR HEAVY METAL-CONTAMINATED SOILS BY LASER-INDUCED BREAKDOWN SPECTROSCOPY Alexander, Dennis R.; Dana E. Poulain, Nebraska Univ., Lincoln NTIS: ADA328435. 34 pp, Jun 1997 Laser-induced breakdown spectroscopy (LIBS) is a rapid remote measurement method for detection of metals in the environment. A major factor in the quantitative use of this technique involves the minimum detection limits under both laboratory and field operations. Research on limits of detection of heavy metals in different types of soils under various conditions using LIBS has been carried out. Pulses from a Nd:YAG laser operating at 125 mJ at lambda = 1.06 micrometers are focused on sample surfaces to produce laser sparks (plasmas). Atomic emissions from the plasmas are recorded using an optical multichannel analyzer after delays of a few microseconds when interference from broad-band emissions is reduced. Research has been performed on the detection limits of arsenic, cadmium, chromium, mercury, lead, and zinc in soil matrices. Results are reported on the lower detection limits of these six elements in sand, silt, clay, and kaolin matrices. Detection limits are significantly lower for heavy metals in sand matrices than silt and clay matrices due to differences between surface and volume contamination.