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| This report is an archived publication and may contain dated technical, contact, and link information |
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| Publication Number: FHWA-HRT-14-021 Date: January 2014 |
Publication Number: FHWA-HRT-14-021 Date: January 2014 |
Table 16 summarizes the overall number of samples and number of replicates per sample examined in this research. It also provides the mean total, extractable, and bioaccessible arsenic and lead contents measured in the entire sample set of glass beads analyzed in this study. While an intra-method comparison for total arsenic and lead content in the beads did not result in agreement among the four methods evaluated, KOH fusion digestion coupled to ICP-MS analysis reproduced the SRM content of both analytes to within 94 percent of the target value for six samples of SRM analyzed in triplicate. In addition, spiked addition controls demonstrated 106 ± 12 percent recovery of the known addition for both lead and arsenic in all spiked samples when KOH fusion was used. Therefore, the researchers have confidence that KOH fusion followed by ICP-MS analysis is a suitable method for measuring arsenic and lead content in the glass beads.
Arsenic speciation was observed in laboratory-generated samples of leachate under neutral pH conditions. Arsenate (As5+) ranged from 8.9 and 15 µg/L in the leachate solution; whereas arsenite (As3+) was present below 3.0 µg/L in the leachate. Arsenic and lead were also present in bead-impacted soil samples collected from a facility used for more than 20 years to store and transfer beads on site. When present, arsenic had a mean content in the site soils of less than 5.5 ppm. Lead was detected in all of the samples at contents ranging 12 to 120 ppm. (Control site lead content was 24 ppm.) Overall glass content within collected samples from the site ranged from 20 to 78 percent by weight, with an average content of 42 percent by weight.
Based on laboratory and field sample characterization completed in this study, the mean concentrations observed in the beads were below the 200 ppm arsenic and lead limit adopted in the recently approved MAP-21 legislation. Therefore, the proposed limit should not present a hurdle to using existing beads already in the commercial markets for pavement marking purposes.
Table 16. Summary of total, extractable, and bioaccessible arsenic and lead in all of the samples analyzed in this study.
|
Method |
No. of Samples |
No. of Replicates Per Sample |
Arsenic |
Lead |
||
|
Frequency of Reportable Detection (percent) |
Mean Content When Present (ppm) |
Frequency of Reportable Detection (percent) |
Mean Content When Present (ppm) |
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|
Total |
15 |
9 |
100 |
54 |
100 |
71 |
|
Extractable |
15 |
3 |
0 |
— |
47 |
0.8 |
|
Bioaccessible |
15 |
3 |
0 |
— |
20 |
1.8 |
ppm = parts per million
— indicates not detected in any sample
