Chemical safety is assessed by the relationship of toxic effects to exposure concentrations, that is, by defining the margin of safety. To date, however, these principles have been applied only to organisms in the water column of aquatic ecosystems. A deficiency exists in our ability to understand the aquatic hazard of chemicals that are sorbed to sediment. Studies to define the key route of exposure (interstitial water, water column water, sediment or food) were conducted with Kepone and the midge, Chironomus tentans, in partial life cycle static and flow-through tests. The endpoints measured were survival, growth, and bioaccumulation. Seven separate 14-day partial life cycle tests were conducted. The no effect-effect concentrations for midges exposed to Kepone in the water were >5.4 <11.8 ppb. No effects were observed when the midges were fed food containing up to 17 900 ppb Kepone. In the sediment exposure studies, the no-effect concentrations varied from 3000 to 36 000 ppb depending upon the organic carbon content of the sediment. In all the sediment exposure studies, water column concentrations were below the water exposure chronic effect levels (11.8 ppb), and effects were observed only when the sediment interstitial column concentrations exceeded the 11.8 ppb water column exposure chronic effect level. Measured bioaccumulation factors for each study showed little variability when the midge tissue concentrations were divided by the sediment interstitial water concentrations. Calculations of the bioaccumulation factors based on water column concentrations or sediment concentrations were highly variable. It can be concluded from our studies with Kepone and C. tentans that the key route of exposure is from the interstitial water and/or the water at the sediment/water interface. Toxic effects can be expected to occur in benthic invertebrates only if the chemical concentration is high enough in the sediments such that the equilibrium interstitial water concentration reached by desorption is equal to or higher than the concentration demonstrated to cause an effect in a water exposure test. Interpretation of aquatic hazard and calculation of safety factors for nonionic organic chemicals sorbed to sediments should be based on the concentration of the chemical in the sediment interstitial water, which is a function of the chemical's sediment partition coefficient (Kp), concentration of chemical on the sediment, and the organic carbon content of the sediment.
ABSTIXACTThe biocnergctic role of a population of Glyptotendipes bnrhipes in the process of waste stabilization in two sewage lagoons was studied. Weekly production rates of the multivoltine midge were computed. Annual production of G. barbip.es was 808 kcal/m" in a narrow band ncarshore of the secondary lagoon containing 90% of the biomass.Biomass data from both lagoons in 1966 and 1967 were used to estimate production using a turnover ratio (TR) of 8.49 (ratio of production: mean biomass) from definitive data collected in 1967. Production in the secondary lagoon was 459 kcal/m2 in 1966 and 37 in 1967; in the primary lagoon it was 165 and 18 respectively. The factors causing these differences in production were probably the dissolved oxygen concentrations during the growing season, percent of the total lagoon bottom inhabitable by midge larvae, and the condition of the sludge substrate.The total energy removed by emergence and respiration of G. barbipes was compared with the energy in other pathways in the lagoon: import of sewage, primary production, community respiration, storage, and export. In 1966, G. burbipes removed about 6.6% of the net primary production in the secondary lagoon and 0.5% in 1967.
A nine-laboratory round-robin study of the Duphniu mugnu static, acute, effluent toxicity test was conducted to examine inter-and intralaboratory variability in test results. A single effluent sample was split and sent to three government, three commercial and three industrial aquatic laboratories. Each laboratory followed a specifically designed test protocol and reported the number of daphnids immobilized in each of seven effluent test concentrations at 24 h and 48 h of exposure. The mean 48-h EC50 value for all data was 5.3% effluent. The range was 3.5 to 9.1% effluent, so there is a factor of 2.6 between the highest and lowest EC50 values. The pooled within-laboratory standard deviation and coefficient of variation were 0.91 and 1670, respectively. Combined interand intralaboratory estimates of standard deviation and coefficient of variation were 1.8 and 3370, respectively. The results of this study show that Duphniu mugnu effluent toxicity data can be reproduced both within and between laboratories when clearly defined test protocols are employed.
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