Variations in plant and soil lead and mercury content in a major Honolulu Park, 1972 to 1987, a period of significant source reduction
✍ Scribed by Shag-Lian Fu; Harlan Hashimoto; B. Z. Siegel; S. M. Siegel
- Publisher
- Springer Netherlands
- Year
- 1989
- Tongue
- English
- Weight
- 488 KB
- Volume
- 43
- Category
- Article
- ISSN
- 0049-6979
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✦ Synopsis
The Ala M0ana beach and park area in S E Honolulu is exposed to (1) local automotive exhaust emissions from the heavily travelled boulevard and high density shopping mall located immediately to the north; (2) a frequently congested access road located between the park proper and the beach; and (3) a remote source of geothermal and volcanic emissions 400 km to the SE on the Island of Hawaii.
Between 1972 and 1987 both local Pb emissions and the more remote Hg emissions fell by more than 80%. Reductions in Pb reflected declining use of 'leaded' gasoline; reductions in Hg reflected a declining output of Hg ° vapor from volcanic and fumarolic sources.
We compared Pb and Hg contents along a 150 m transect of soil and the grass Cynodon in 1972 and 1987. At the boulevard median divider, where particulate Pb deposition is heaviest, the metal content of the upper 5 to 6 cm of soil was reduced by approximately 53 % but in the main body of the park no consistent pattern was found and an overall 21% reduction was observed. The highest soil Pb values were measured at the boulevard and beach access roads, with lower intermediate levels. The grass shoots showed a similar pattern but overall Pb content fell 65% between 1972 and 1979, a value more consistent with the reduction in Pb contamination from leaded gasoline. Neither soil nor plant Hg contents reflect a strong roadside to interior concentration gradient, but both fell between 1972 and 1987 by 60 and 68%, respectively.
The biogeochemical significance of concentration ratios (plant/soil) and Pb/Hg atomic ratios was examined. With the exception of soil fixation of Pb in a relatively non-mobile soluble form, we conclude that for the two metals, the changes in levels reflect changes in the source (local for Pb and remote for Hg). There is also evidence for physiological regulation in the uptake of the two elements.