The response of trout and zebrafish embryos to low and high boron concentrations is U-shaped.
Fish in the embryo-larval stage of development have been shown to be sensitive to boron (B) at both ends of the dose-response curve (1,2). The present study evaluated the health effects of low and high B concentrations on rainbow trout (Oncorhynchus mykiss), a cold water species, and zebrafish (Danio rerio), a warm water species. Rainbow trout embryos were incubated from day 1 until 2 wk posthatch in Type 1 ASTM ultrapure-grade water (12.5 degrees C) supplemented with only B (0-500 microM) as boric acid, or together with CaCO3 (0-2 mM) to increase water hardness. Embryonic growth was stimulated by B in a dose-dependent manner at all Ca concentrations (p < 0.001). Chronic exposures below 9 micromol B/L impaired embryonic growth and above 10 mmol B/L caused death (p < 0.001). Thus, the safe range of exposure for the rainbow trout was between the adverse effect concentrations of 9 micromol B/L and 10 mmol B/L. Zebrafish were maintained for 6 mo in ultrapure water containing <0.2 micromol B/L to determine the effect of low-level exposure. High-level exposure was assessed by exposing zygotes, derived from parents maintained at 46 micromol B/L, to graded concentrations of boric acid up to a concentration of 75 mmol B/L from fertilization until they were free feeding (96 h). Fertilization occurred, but zygotes failed to survive when water contained <0.2 micromol B/L (p < 0.001). Death occurred at and above 9.2 mmol B/L. Thus, the safe range of B exposure for zebrafish was between the adverse effect concentrations of 0.2 micromol B/L and 9.2 mmol B/L. The dose-response for both species was thus U-shaped.
Department of Environmental Health Sciences, University of California, Los Angeles 90095-1772, USA.
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D000704:Analysis of Variance; D000818:Animals; D001895:Boron / Q000172:deficiency / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D017686:Oncorhynchus mykiss / Q000196:embryology*; D015027:Zebrafish / Q000196:embryology*
D001895:Boron