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Boron may also contribute to toxicity in many western locations because it is frequently elevated wherever selenium is high. The possibility of interactive effects between boron and selenium has been suggested (Hoffman et al. 1988). Boron has a role in the calcium cycle and in respiratory processes and the utilization of carbohydrates. According to recent guidelines, fish reproductive tissues are affected at concentrations on the order of 1 mg/L (USDOI 1998). Boron in water becomes a problem at about 10 mg/L for crops and plants, at 13mg/L for aquatic invertebrates, at 25 mg/L for fish, at 20 mg/L for bird eggs, at >30 mg/L for waterfowl, and at >80 mg/L for mammals (USDOI 1998). Dietary boron in concentrations up to 1,000 ug/g was not teratogenic to mallards, and hatching success was unaffected by boron concentrations up to 300 ug/g. Saiki et al. (1993) evaluated boron in the food chain in conjunction with selenium. The concentration of boron recommended for protection of sensitive aquatic life was exceeded. in several locations, but not by as much as selenium. Fingerling fish were affected by some high- boron tile water, but effects of other ions could not be ruled out. Boron was elevated in plants but did not seem to biomagnify. No effects were observed for molybdenum. This study also demonstrated that, although much variation was present, the highest concentrations of selenium occurred in detritus, mosquitofish, and chironomid larvae. Lower concentrations were measured in other invertebrates and fishes. Filamentous algae generally contained the lowest concentrations of selenium measured in biota. Compared with biota, water and sediment contained little selenium. This study also demonstrated that boron and. selenium were often, but not always, correlated to conductance, turbidity, pH, total alkalinity, total dissolved solids (TDS), and total hardness. Fish tissue concentrations have often been used as diagnostic for selenium poisoning, although researchers agree that eggs are a better indicator. Nevertheless, concentrations in tissue suggest differences in selenium uptake either among species or related to different environments. For example, at Belew's Lake, it was reported that 5-10 ug/g of selenium in muscle was an indicator that the bullheads, carp, and green sunfish were sterile (Lemly 1985). However, green sunfish and carp are reproducing at Sweitzer Lake in western Colorado, and tissue concentrations of 15-25 ug/g have been measured in the sunfish, with 30-40 ug/g having been measured in carp (Butler et al. 1991). It is also of interest to note that western Colorado's Crawford Reservoir, a lake known for its overabundance of yellow perch, yielded a perch fillet with 16 ug/g dry weight of selenium (Butler et al. 1994). In a later report in the Grand Valley, fish samples were frequently found exceeding the 5-10 ug/g cited above by Lemly (1985). Butler et al. (1994) also noted that the "selenium concentrations in whole-body fathead minnows in the middle Grand Valley ranged from 8 ug/g dry weight to 22 ug/g dry weight and. exceeded known toxicity concentrations to fathead minnows of 6 ug/g dry weight." Butler et al. (1994) listed two citations (Ogle and Knight 1989; Schultz and Hermanutz 1990) for the 6 ug/g toxicity figure-a value that is low in comparison with Lemly's finding at Belew's Lake as discussed above (1985). Such data clearly indicate that there are unsettled issues regarding species sensitivity and the concentrations of selenium at which fish are affected. Values of selenium in fish eggs also provide some confusing results. Lemly (1996) has stated that >20 ug/g represents a high hazard for reproductive impairment in fish. A study by Hamilton et al. (1997) showed that egg concentrations from fish in some Grand Valley backwaters were as high as 30-40 ug/g. Nevertheless, larval survival was 70% if the larvae were transferred to