PARENT SESSION
PW10 - Ecological Risk Assessment
Wednesday, 20 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P836) Ecological hazard assessment of boron: Consideration for aquatic and terrestrial risk assessments.
Schlekat, Christian*,1, Robinson, Sue2, DeForest, David2, Phipps, Terry2, Hubbard, Susan3, 1 U.S. Borax, Inc., Valencia, CA, USA2 Parametrix, Inc., Kirkland, WA, USA3 Borax Europe, Ltd., Guildford, UK, UK
ABSTRACT- Boron occurs naturally in terrestrial and aquatic environments, and exists in the environment almost exclusively as compounds called borates. Borates are used in many commercial and industrial applications, from which some level of exposure to aquatic and terrestrial ecosystems occurs. The goal of this presentation is to review the hazard of boron in aquatic and terrestrial habitats, and to provide guidance for ecological risk assessments of boron. In aquatic environments, boric acid (B(OH)3) is the predominant form under typical pH ranges. The most sensitive aquatic species is the rainbow trout (Oncorhynchus mykiss), an organism that has also been demonstrated to require boron for proper development. The representativeness of the lowest reported toxicity values (1.3 mg B/L) are debatable as natural populations of O. mykiss successfully propagate in waters containing > 5.0 mg B/L. Furthermore, chronic toxicity values for invertebrates and plants are at least 7.5 times higher. Careful judgement is therefore necessary when choosing effects concentrations for aquatic risk assessments. Boron concentrations in aquatic biota generally do not exceed water concentrations by more than a factor of 150, indicating a low potential for bioaccumulation. Bioavailability of B(OH)3 appears to be affected by pH and DOC. Finally, low distribution coefficients of B(OH)3 (<100) minimize accumulation in sediments. In terrestrial environments, boron occurs as borate minerals and as B(OH)3 in the aqueous phase of soil. Soil invertebrates appear tolerant of B(OH)3 exposure, although data are limited. Although the literature on boron toxicity to plants is broad, boron is also an essential plant nutrient. Therefore, effects concentrations should be chosen on a site-specific basis. While some plants bioaccumulate boron, effects concentrations via dietary ingestion for herbivorous birds and mammals are above observed concentrations. Significant data gaps in the boron ecotoxicity literature will be identified, as will strategies for addressing these gaps.
Key words: boron, risk assessment, aquatic, soil