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- Table 18. Summary of freshwater fish toxicity data (TLm mg/L) for MMT
- Table 19. Summary of freshwater fish toxicity data for manganese
m.5Fishm.5.1MMTThe acute (96-hour) toxicity of MMT was studied in two species of freshwater fish - Bluegill sunfish (Lepomis macrochirus) and Fathead Minnow (Pimphales promelas) under static test conditions (Kem-Tech Laboratories, 1977). Bioassays were conducted with three applied concentrations of MMT with 10 fish in 12 litres (in 20 litre glass cylinders). Test dilution water had a hardness of approximately 125 ppm (as CaCO3), pH 7.0 and dissolved oxygen (saturated). Light was limited as much as practical during the tests with MMT. The fish were conditioned to semi-dark conditions at 20C. MMT was added to the medium with acetone as solvent. The Kem-Tech Laboratories (1977) study was undertaken in duplicate with measured MMT concentrations (means) of <0.04 (control), 0.14, 0.25 to 0.36, and 0.45 to 0.47 mg/L. Measured concentrations were less than estimated nominal concentrations, presumably due to both spontaneous degradation of MMT and MMT degradation associated with contact with fish. MMT concentrations in each test solution declined significantly throughout the test duration. Median Threshold Limit (TLm or TL50) is the concentration of a chemical estimated to kill 50% of exposed organisms in a given time period. It is often used interchangeably with aquatic LC50 (USEPA, 1977). TLm concentrations (measured, mg/L) over 12, 24, 48, 72 and 96 hours for L. macrochirus and P. promelas are summarised in Table 18.
As indicated above, most lethality occurred within the first 12 hours. Mortality was rare in the initial hour in tests under 3 ppm (measured). However, stress was evident in the first few minutes (Kem-Tech Laboratories, 1977). The constancy of effects through time probably reflects the rapid degradation of MMT from the test solutions. Monitoring of MMT in test solution indicated 80 to 88% reduction in MMT within a 96-hour period. TLm results beyond 12 hours are probably not reliable. The lowest 12-hour TLm derived for MMT was 0.20 mg/L. Sensitivity to MMT was similar between the species, with mortality evident in the concentration of 0.18 to 0.34 mg/L or greater. Survival was evident below an exposure concentration of 0.18 mg/L. However, stress (irritation) was evident in fish at the lowest test concentration (0.14 mg/L). The threshold for stress was not determined. Recovery from stress was evident following cessation of exposure. The mode of toxicity in both fish species tested was similar with symptoms including fitful activity, gradual loss of equilibrium (horizontally usually first, then vertically), excess mucous production except in the lowest test concentrations, and finally gulping at the surface with fitful swimming. Acknowledging data limitations, these results suggest that MMT may be considered highly toxic to fish, with acute LC(EC)50 values in the range of <1 mg/L (Mensink et al., 1995). m.5.2ManganeseThe data presented below indicate that Mn is slightly to moderately toxic to freshwater fish with acute and chronic LC(EC)50 values in the range of 10 to 100 and 1 to 10 mg/L, respectively (Mensink et al., 1995). Several studies have investigated the effects of Mn on freshwater fish. ANZECC and ARMCANZ (2000) reported acute (48 to 96-hour) LC50 values of 33.8 to 4540 mg/L. Several data are available on the effects of chronic exposure of freshwater fish to Mn, and chronic NOEC values in the range of 1.27 to 9.99 mg/L (growth and mortality). The toxicity data have been summarised in Table 19. Table 19. Summary of freshwater fish toxicity data for manganese
a - Maximum acceptable threshold concentration (MATC) is a hypothetical threshold concentration that is the geometric mean between the NOEC and LOEC concentration. b - Range not refined. c. Water hardness dependent (refer below). Stubblefield et al. (1997), as cited by USEPA (2000), determined that water hardness significantly affects Mn chronic toxicity, with toxicity decreasing with increasing hardness. Using early life stage brown trout (Salmo trutta), Stubblefield et al. (1997) derived 62-day 25th percentile inhibitory concentration (IC25) values, based on the combined endpoints (i.e., survival and body weight), were 4.67, 5.59, and 8.68 mg/L (based on measured Mn concentrations) at hardness levels of approximately 30, 150, and 450 mg/L as CaCO3, respectively. NOEC values (62-day) for mortality and growth were 4.41 mg/L and 4.55 mg/L, respectively. No toxicity data were available on the effects of Mn on saltwater fish species.
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