Current and historic mercury deposition to New Haven Harbor (CT, USA): implications for industrial coastal environments.

This study quantifies historic and current mercury contamination in New Haven Harbor (New Haven, Connecticut, USA) through the analysis of sediment cores. The mercury concentration measured in surface sediment ranged from 320 to 1640 microg kg(-1) with an average of 530 microg kg(-1). The harbor is relatively small in area (6.6 km(2)) but displays a large range in concentrations, illustrating the important methodological issue that a large number of samples may be necessary to capture the variability in even a small area. Depth profiles of mercury reflect sedimentation over a range of 20 to 200 years and indicate a complex history of contamination. Mercury depth profiles were compared with lead, copper, cadmium, and silver concentrations and the metals generally covary. This trend indicates that the sources of mercury and heavy metals are linked and that regionally specific sources dominate the historic input of metals rather than large-scale atmospheric deposition patterns. Results also show there are large differences in absolute concentrations of metals among sites in the harbor. Differences in the abundance of Fe-rich, fine-grained sediment likely control the level of metals in various parts of the harbor. Proximity to current sources and the long, diverse industrial history of the harbor also influence the distribution pattern. All of the cores can be modeled as mixing between pre-industrial sediments and either one or two pollution endmembers. This study demonstrates the importance of riverine sources in the mass balance of mercury delivered to coastal areas and of watershed management to preserve coastal ecosystems.

Urban gardens: lead exposure, recontamination mechanisms, and implications for remediation design.

Environmental lead contamination is prevalent in urban areas where soil represents a significant sink and pathway of exposure. This study characterizes the speciation of lead that is relevant to local recontamination and to human exposure in the backyard gardens of Roxbury and Dorchester, MA, USA. One hundred forty-one backyard gardens were tested by X-ray fluorescence, and 81% of gardens have lead levels above the US EPA action limit of 400 microg/g. Raised gardening beds are the in situ exposure reduction method used in the communities to promote urban gardening. Raised beds were tested for lead and the results showed that the lead concentration increased from an initial range of 150+/-40 microg/g to an average of 336 microg/g over 4 years. The percent distribution of lead in the fine grain soil (<100 microm) and the trace metal signature of the raised beds support the conclusion that the mechanism of recontamination is wind-transported particles. Scanning electron microscopy and sequential extraction were used to characterize the speciation of lead, and the trace metal signature of the fine grain soil in both gardens and raised gardening beds is characteristic of lead-based paint. This study demonstrates that raised beds are a limited exposure reduction method and require maintenance to achieve exposure reduction goals. An exposure model was developed based on a suite of parameters that combine relevant values from the literature with site-specific quantification of exposure pathways. This model suggests that consumption of homegrown produce accounts for only 3% of children's daily exposure of lead while ingestion of fine grained soil (<100 microm) accounts for 82% of the daily exposure. This study indicates that urban lead remediation on a yard-by-yard scale requires constant maintenance and that remediation may need to occur on a neighborhood-wide scale.

Sources, sinks, and exposure pathways of lead in urban garden soil.

The chemistry of Pb in urban soil must be understood in order to limit human exposure to Pb in soil and produce and to implement remediation schemes. In inner-city gardens where Pb contamination is prevalent and financial resources are limited, it is critical to identify the variables that control Pb bioavailability. Field-portable X-ray fluorescence was used to measure Pb in 103 urban gardens in Roxbury and Dorchester, MA, and 88% were found to contain Pb above the USEPA reportable limit of 400 mug g(-1). Phosphorus, iron, loss on ignition, and pH data were collected, Pb-bearing phases were identified by X-ray diffraction, and Pb isotopes were measured using inductively coupled plasma mass spectrometry. Four test crops were grown both in situ and in Roxbury soil in a greenhouse, and plant tissue was analyzed for Pb uptake by polarized energy-dispersive X-ray fluorescence. Variation at the neighborhood scale in soil mineralogical and chemical characteristics suggests that the bioavailable fraction of Pb in gardens is site specific. Based on Pb isotope analysis, two historical Pb sources appear to dominate the inventory of Pb in Roxbury gardens: leaded gasoline ((207) Pb/(206) Pb = 0.827) and Pb-based paint ((207)Pb/(206) Pb = 0.867). Nearly 70% of the samples analyzed can be isotopically described by mixing these two end members, with Pb-based paint contributing 40 to 80% of the mass balance. A simplified urban human exposure model suggests that the consumption of produce from urban gardens is equivalent to approximately 10 to 25% of children's daily exposure from tap water. Furthermore, analysis of over 60 samples of plant tissue from the four test species suggests that in these urban gardens unamended phytoremediation is an inadequate tool for decreasing soil Pb.