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National Irrigation Water Quality Program Guidelines I I borate or boric acid) are rapidly and almost completely absorbed from the gastrointestinal tract, do not seem to accumulate in healthy tissues, and are excreted in urine, usually within hours (NAS 1980; Benson et al. 1984; Nielsen 1986; Siegel and Wason 1986). Bioaccumulation Boron can be bioconcentrated to varying degrees by aquatic organisms (Ohlendorf et al. 1986). Green algae (Chlorella pyrenoidosa) had a bioconcentration factor of 5 (boron concen- tration five times the level in the surrounding medium) after being exposed to a 50-100 mg BIL boric acid solution for 7 days (Fernandez et al. 1984). In the San Joaquin Valley, filamentous algae accumulated 390-787 mg Blkg when exposed to brackish tile drainage containing 12-41 mg BIL, and they accumu- lated 64-140 mglkg when exposed to fresher water containing 1.4-2.2 mglL (Schuler 1987). Aquatic insects living in the tile drainage contained 22-340 mg Blkg, but those living in fresh water untainted by agricultural tile drainage contained 6-47 mgl kg (Ohlendorf et al. 1986; Schuler 1987; Hothem and Ohlendorf 1989). Lenma species are outstanding boron bioaccumulators. Proficiency in boron stripping coupled with a high growth rate distinguishes Lenll1a minor as an important species with respect to boron cycling in a freshwater macrophyte community. The effectiveness of this species in consuming boron may be a potent force in lowering the concentrations of this essential element in aquatic systems (Glandon and McNabb 1978). Frick (1985) determined that pH affected the bioaccumulation of boron in Lenmt1 minor, indicating that chemical speciation of boron may affect bioaccumulation and toxicity. Interactions Hoffman et al. (1991) examined boron- selenium interaction effects in mallard 0fJ ducklings under two very different conditions: (1) a protein-adequate diet and (2) an iso- caloric protein-deficient diet. Unquestionable interaction effects were noted only under conditions of protein deficiency. However, Hoffman et aJ.'s protein-deficient diet was unlike any likely to be encountered by ducklings in the wild, so the results for part 2 of their experiments are essentially irrelevant to these guidelines. The results of part 1 are more relevant to the real world and failed to reveal any substantive interaction effects (despite unrealistically high dosing levels). More recently, Stanley et al. (1996) experimentally studied the effects of boron- selenium interactions on mallard reproductive performance, duckling growth, and duckling survival. Their experiments also found little evidence of interaction between these elements. I I I I I I I I Regulatory Standards U.S. Environmental Protection Agency standards and criteria [See Appendix \I for explanation of terms. Source: EPA 1995} Status listed for regulation; carcinogenicity unknown Drinking water Not established MCL Drinking water 1-day HA: 4 mglL health advisories 10-day HA: 0.9 mg/L for 1 O-kg child Long-term HA: 0.9 mglL Drinking water Reference dose: 0.09 mglkgld health advisories Long-term HA: 3 mglL for 70-kg adult lifetime HA: 0.6 mglL DWEL: 3 mglL I I I I I For standards and criteria set by State agencies, contact those agencies directly. See Appendix I for a listing of water-quality officials in the 17 Western States. I I I I