Oahu Soil & Sediment As

Distribution & Abundance of Arsenic (As) in the Soils &

Sediments of Oʻahu, Hawaiʻi

Michael S. Tomlinson, Eric H. De Carlo, Sara Thomas, & Laura E. deGelleke

Oʻahu, Hawaiʻi

Oʻahu

Hawaiʻi

Maui

Kauaʻi

Molokaʻi

Lānaʻi

Kahoʻolawe

Niʻihau

Ordnance Reef Remedial Investigation

Diamond Head

Honolulu Barbers Point

Kaʻena Point

Kahuku Point

Makapuʻu Point

Kailua

Kāneʻohe

Māmala Bay

Waiʻanae

Ordnance Reef RI – Where did the As come from?

Nonmetric Multidimensional Scaling (NMDS)

Anomalous [As] were seen in bed sediments during USGS NAWQA Study

A = Agriculture

F = Forested

U = Urban

M = Mixed

Anthropogenic Trace Elements?

???

Arsenical Pesticides (e.g., NaAsO2), Super-phosphate Fertilizers?

Principal Component Analysis

Anomalous [As] were reported in soil data compiled by HIDoH

Arsenic Sources & Transfer

Oʻahu Relief, Isohyets, & UHM Samples

As & Former Sugarcane Land

As & Former/Current Pineapple Land

As in Waiakeakua Stream

Why is arsenic in Waiakeakua

Stream?

Where does the arsenic come from?

Possibly iron & zinc micronutrient fertilizer from silver mine tailings used by nurseries to green-up plants (Human Health Risk Assessment for Long-term Residential Use of Ironite® Lawn and Garden Nutrient Supplement - ADEQ, 1998)

Conclusions

• As occurs in nearshore Oʻahu sediments

• NMDS indicates a loose association with terrestrial elements (probably from runoff)

• As occurs in some NAWQA stream sediments associated with agriculture

• PCA of NAWQA sediments indicate a loose association with petrogenic elements but not anthropogenic elements

• HIDoH data show elevated [As] but the distribution is spotty

Conclusions (continued)

• Some As may be associated with past sugarcane and/or pineapple agriculture (arsenical pesticides – ceased late 1940s, super-phosphate fertilizers, etc.)

• The highest [As] on Oʻahu, however, are found in mixed land use/forested areas

• Arsenical pesticides & micronutrient fertilizers (e.g., Ironite®) used in nurseries may explain some As

• And, finally …

Yes, arsenic occurs naturally in Arizona, however, do not totally discount

anthropogenic sources

Photo taken in Flagstaff Sam’s Club

Mahalo nui loa! Questions?

Mālama i ko mākou ʻāina (Care for our land)