Céline Gallon

Asian Industrial Lead Inputs to the North Pacific Evidenced by Lead Concentrations and Isotopic Compositions in Surface Waters and Aerosols

Recent trends of atmospheric lead deposition to the North Pacific were investigated with analyses of lead in aerosols and surface waters collected on the fourth Intergovernmental Oceanographic Commission Contaminant Baseline Survey from May to June, 2002. Lead concentrations of the aerosols varied by 2 orders of magnitude (0.1-26.4 pmol/m(3)) due in part to variations in dust deposition during the cruise. The ranges in lead aerosol enrichment factors relative to iron (1-119) and aluminum (3-168) were similar, evidencing the transport of Asian industrial lead aerosols across the North Pacific. The oceanic deposition of some of those aerosols was substantiated by the gradient of lead concentrations of North Pacific waters, which varied 3-fold (32.7-103.5 pmol/kg), were highest along with the Asian margin of the basin, and decreased eastward. The hypothesized predominance of Asian industrial lead inputs to the North Pacific was further corroborated by the lead isotopic composition of ocean surface waters ((206)Pb/(207)Pb = 1.157-1.169; (208)Pb/(206)Pb = 2.093-2.118), which fell within the range of isotopic ratios reported in Asian aerosols that are primarily attributed to Chinese industrial lead emissions.

All the Lead in China

Lead contamination in China has been extensively documented by scientists in China and elsewhere over the past two decades, as summarized in this review of articles published in peer-reviewed scientific journals. Sources of that contamination include (a) deposits from previous emissions of leaded gasoline, which was finally eliminated in the past decade; (b) previous and continuing emissions from fossil fuel combustion, which are increasing markedly with the rapid industrialization of China; (c) previous and continuing emissions from other industrial activities, including mining, smelting and municipal waste incineration; and (d) previous and continuing additions of contaminated fertilizers, sewage, and untreated wastewater to agricultural fields. Lead concentrations of some Chinese agricultural produce are also elevated by acid rain and acidic fertilizers, which increase the solubility and bioavailability of both natural and contaminant lead in soil. In addition, some Chinese products are contaminated with lead during their production, processing, packaging, and transport. As a consequence of the long-range transport of industrial lead emissions from China and the global market for its products, the problem of lead pollution in China is a global problem.

Surviving in anoxic surroundings: how burrowing aquatic insects create an oxic microhabitat

Abstract We used an infrared video system and O2 microelectrodes to record the behavior of 2 widespread burrowing insects, the predatory alderfly Sialis velata and the sediment-feeding mayfly Hexagenia limbata, to determine how they survive in anoxic sediment. Analysis of video recordings showed that both taxa have several common behaviors, including crawling, pushing sediment, turning around, and brushing their legs over their bodies for the purpose of cleaning. In contrast, these taxa differ in how they draw overlying oxic water into their burrows, i.e., H. limbata beats its abdominal gills, whereas S. velata undulates its abdomen. Feeding frequency also differs between the 2 taxa, i.e., the mayfly feeds frequently on sediment within its burrows, whereas S. velata feeds infrequently. Hexagenia limbata nymphs were rarely inactive (<1% of the time) and irrigated their burrows by gill-beating ¾ of the time, whereas S. velata nymphs were usually inactive (60% of the time). By vigorous irrigation of its burrow, H. limbata maintained its surroundings well oxygenated, whereas O2 concentrations fluctuated more widely in burrows of the less-active S. velata. This behavioral difference between the species is consistent with their reported sensitivities to the low O2 concentrations associated with eutrophication; in such situations, H. limbata is likely to be eliminated, whereas S. velata can persist. We estimate that O2 lost from water passing through an H. limbata burrow is taken up mainly by the insect rather than diffusing into the surrounding sediment.

Comparison of Mass Discrimination Correction Methods and Sample Introduction Systems for the Determination of Lead Isotopic Composition Using a Multicollector Inductively Coupled Plasma Mass Spectrometer

The influence of sample introduction system on Neptune MC-ICPMS lead isotopic ratio measurements was tested on dilute solutions of the lead certified material NIST SRM 981 ([Pb] = 0.2-170 ng g(-1)) using (1) a SIS spray chamber, (2) a MCN 6000 desolvating system, or (3) an Apex inlet system. The impact of using a high-efficiency X-cone in place of a standard H-cone with the MCN and Apex was also investigated. Performance of the sample introduction systems varied with lead concentration. Over 10 ng g(-1), no system was significantly more precise or accurate. As lead concentrations decreased, both accuracy and precision diminished, and below 1 ng g(-1), use of an X-cone in combination with the Apex and particularly with the MCN system notably improved the quality of the measurements. Various mathematical methods of mass bias correction using thallium additions were tested. Selection of (205)Tl/(203)Tl for NIST SRM 997 to optimize data (1) daily, (2) for each introduction system, and (3) over all sessions significantly improved the data, with no major difference in the output between the three methods. Consistency of the (205)Tl/(203)Tl ratio (2.3888) optimized over all data with previous observations by others supports the use of this value for future measurements.

A new method for stable lead isotope extraction from seawater.

A new technique for stable lead (Pb) isotope extraction from seawater is established using Toyopearl AF-Chelate 650M(®) resin (Tosoh Bioscience LLC). This new method is advantageous because it is semi-automated and relatively fast; in addition it introduces a relatively low blank by minimizing the volume of chemicals used in the extraction. Subsequent analyses by HR ICP-MS have a good relative external precision (2σ) of 3.5‰ for (206)Pb/(207)Pb, while analyses by MC-ICP-MS have a better relative external precision of 0.6‰. However, Pb sample concentrations limit MC-ICP-MS analyses to (206)Pb, (207)Pb, and (208)Pb. The method was validated by processing the common Pb isotope reference material NIST SRM-981 and several GEOTRACES intercalibration samples, followed by analyses by HR ICP-MS, all of which showed good agreement with previously reported values.

Historic and Industrial Lead within the Northwest Pacific Ocean Evidenced by Lead Isotopes in Seawater

We report the continued lead (Pb) contamination of the Northwest Pacific Ocean in 2002 and present the first comprehensive Pb isotope data set for that region. In the upper ocean, a Pb concentration maxima (64-113 pmol kg-1) extended throughout the entire North Pacific Subtropical Gyre (NPSG). We determined most of the Pb in this feature was from industrial emissions by many nations in the 1980s and 1990s, with the largest contributions from leaded gasoline emissions. In contrast, the deep water (>1000 m) Pb concentrations were lower (6-37 pmol kg-1), and constituted a mix of background (natural) Pb and anthropogenic Pb inputs from preceding decades. Deep water below the Western Subarctic Gyre (WSAG) contained more industrial Pb than below the NPSG, which was attributed to a calculated 60-fold greater flux of particulate Pb to abyssal waters near the Asian continent. Assuming Pb isotope compositions in the North Pacific Ocean were homogeneous prior to large-scale 20th century anthropogenic inputs, this evidence suggests a relatively faster change in Pb isotope ratios of North Pacific deep water below the WSAG versus the NPSG.