Temporal Changes in Lead Bioaccessibility in Newly
Temporal Changes in Lead Bioaccessibility in Newly Deposited, Floodplain Sediments
0631
Chris Morrow, Daniel G. Strawn, Leslie L. Baker, Anita Falen Soil and Land Resources Division, University of Idaho Introduction:
Sediment Sampling
Temporal and Spatial Lead Bioaccessibility:
Over a century of mining activity in the Coeur d’Alene (CDA) River Valley has contaminated the watershed with Pb, Zn, As, and Cd. Soils with high Pb concentrations pose risks to humans, fish, and birds in the region.
The 2008 samples were taken from sediments that were uniformly deposited across the floodplain during the 2008 flood. The 2008 organic mat was clearly visible during the 2010 sampling period at a depth of ~1‐5 cm. Total elemental concentrations were measured using ICP‐OES with HF digestion. Bioaccessible contaminants were measured using ICP‐ OES with TCLP digestion (EPA, 1992). Organic Carbon was measured using Elementar vario MAX CN, and soil particle size was determined using standard UI PSES protocol.
Bioaccessible lead was inversely proportional to total carbon. Between 5% and 10% of total lead was bioaccessible in organic carbon‐rich soils (the silt loams). Between 30% and 40% of total lead was bioaccessible in organic carbon‐poor soils (the sandy loams). There was a notable relationship between the proximity of the soil classes to the river and bioaccessible lead, with samples taken farther from the river having more carbon and less bioaccessible lead. Thus lead bioaccessibility is not only affected by time, but also by site factors such as total carbon and distance from the riverbank.
Periodic flood events remobilize contaminated sediments from the river bottoms and banks and redeposit them in the CDA River Basin floodplain. The goal of this research was to investigate how lead bioaccesibility in sediments changes over time.
Schlepp Field , June 2010 Lead Concentrations: Total and bioavailable lead in the CDA River Basin soil is above EPA minimum cleanup limits. The total lead concentration at both sites dropped by a maximum of 13% between 2008 and 2010. Average bioaccessible lead decreased 20% overall. Depending on the distance between the river and the sub‐sample site, bioaccessible lead varied from +33% to ‐72% over two years between both sites.
Methodology: Two sites were chosen in the CDA river valley, Killarney Lake and Schlepp Field. Newly deposited sediments were sampled immediately after a flood in April 2008. To assess changes occurring over time, the sediments were re‐sampled in June 2010, prior to a subsequent flood.
Killarney Lake Site
Schlepp Field Site
Correlations:
Conclusion:
Bioaccessible lead was found to be inversely proportional to percent silt and percent clay, and directly proportional to percent sand. The observations that silt loam soils consist of less vegetative matter than sandy loam soils, and the proximity of each soil class to the river, suggests that there is also a spatial dependence for bioaccessible lead.
These findings show that varying particle size distribution, proximity to river, and soil carbon are important factors that will affect the bioaccessibility of Pb in newly deposited floodplain sediments. In this case, organic carbon‐poor sandy loam soils closest to the river had higher bioaccessible lead than organic carbon‐rich silt loam soils farther from the river. Further studies need to be conducted to investigate how physicochemical properties change over time, and subsequently affect contaminant bioavailability in order to discern the long‐term fate of Pb in contaminated soils.
0631
Chris Morrow, Daniel G. Strawn, Leslie L. Baker, Anita Falen Soil and Land Resources Division, University of Idaho Introduction:
Sediment Sampling
Temporal and Spatial Lead Bioaccessibility:
Over a century of mining activity in the Coeur d’Alene (CDA) River Valley has contaminated the watershed with Pb, Zn, As, and Cd. Soils with high Pb concentrations pose risks to humans, fish, and birds in the region.
The 2008 samples were taken from sediments that were uniformly deposited across the floodplain during the 2008 flood. The 2008 organic mat was clearly visible during the 2010 sampling period at a depth of ~1‐5 cm. Total elemental concentrations were measured using ICP‐OES with HF digestion. Bioaccessible contaminants were measured using ICP‐ OES with TCLP digestion (EPA, 1992). Organic Carbon was measured using Elementar vario MAX CN, and soil particle size was determined using standard UI PSES protocol.
Bioaccessible lead was inversely proportional to total carbon. Between 5% and 10% of total lead was bioaccessible in organic carbon‐rich soils (the silt loams). Between 30% and 40% of total lead was bioaccessible in organic carbon‐poor soils (the sandy loams). There was a notable relationship between the proximity of the soil classes to the river and bioaccessible lead, with samples taken farther from the river having more carbon and less bioaccessible lead. Thus lead bioaccessibility is not only affected by time, but also by site factors such as total carbon and distance from the riverbank.
Periodic flood events remobilize contaminated sediments from the river bottoms and banks and redeposit them in the CDA River Basin floodplain. The goal of this research was to investigate how lead bioaccesibility in sediments changes over time.
Schlepp Field , June 2010 Lead Concentrations: Total and bioavailable lead in the CDA River Basin soil is above EPA minimum cleanup limits. The total lead concentration at both sites dropped by a maximum of 13% between 2008 and 2010. Average bioaccessible lead decreased 20% overall. Depending on the distance between the river and the sub‐sample site, bioaccessible lead varied from +33% to ‐72% over two years between both sites.
Methodology: Two sites were chosen in the CDA river valley, Killarney Lake and Schlepp Field. Newly deposited sediments were sampled immediately after a flood in April 2008. To assess changes occurring over time, the sediments were re‐sampled in June 2010, prior to a subsequent flood.
Killarney Lake Site
Schlepp Field Site
Correlations:
Conclusion:
Bioaccessible lead was found to be inversely proportional to percent silt and percent clay, and directly proportional to percent sand. The observations that silt loam soils consist of less vegetative matter than sandy loam soils, and the proximity of each soil class to the river, suggests that there is also a spatial dependence for bioaccessible lead.
These findings show that varying particle size distribution, proximity to river, and soil carbon are important factors that will affect the bioaccessibility of Pb in newly deposited floodplain sediments. In this case, organic carbon‐poor sandy loam soils closest to the river had higher bioaccessible lead than organic carbon‐rich silt loam soils farther from the river. Further studies need to be conducted to investigate how physicochemical properties change over time, and subsequently affect contaminant bioavailability in order to discern the long‐term fate of Pb in contaminated soils.
