In laboratory studies, Daphnia magna were exposed for 6 h to five polycyclic aromatic hydrocarbons (PAH) (0.1–2.0 μg/L) in water with and without Aldrich® humics (2 mg DOC/L). Compared to results in nonhumic water, accumulation of PAH by Daphnia in water with humics was significantly reduced for benzo[a]pyrene (−25%) while it was increased for methylcholanthrene (+210%). Humics did not significantly alter Daphnia accumulation of anthracene, dibenzanthracene or dimethylbenzanthracene. In additional studies, humics reduced Daphnia accumulation of benzo[a]pyrene (B[a]P) over a range of B[a|P concentrations (1.1–5.4 μg/L) exceeding the reported limit for water solubility (1.1–1.2 μg/L). Humics consistently increased Daphnia accumulation of methylcholanthrene (MC) over a range of humic concentrations from 0.2 to 10.0 μg DOC/L. Particulates and DOC (10–12 mg TOC/L) occurring naturally in two South Carolina streams reduced Daphnia accumulation of B[a]P by 38–66%, with about 40% of the overall reduction attributable to DOC. We conclude that dissolved refractory organics may significantly affect bioavailability and environmental transport of some PAH in fresh waters.
Field studies demonstrate that the gorgonian coral Leptogorgia virgulata assumes a fan-shaped morphology oriented at right angles to prevailing tidal currents. Laboratory studies using a recirculating water tunnel and Artemia salina nauplii as food show that fan-shaped colonies oriented perpendicular to water currents capture more Artemia per unit time than the same colonies oriented parallel to water currents. Several feeding strategies which may operate at various current speeds are suggested. Possible mechanisms controlling feeding response and the selective advantage of colony morphology and orientation as related to feeding and resistance to hydrodynamic forces are discussed.
Uptake and depuration kinetics for benzo(a)pyrene (B(a)P) were determined for the midge Chironomus riparius (Diptera) with one and two compartment models. Nonfeeding animals were exposed to nominal 1.0 microgram.L-1 14C- B(a)P for eight hr. Depuration over eight hr was determined in animals with and without substrate. The uptake rate constant was 214 +/- 20 hr-1 (X +/- SE, n = 3), while elimination rate constants for the first four hr were 0.22 hr-1 (with substrate) and 0.06 hr-1 (without substrate). Biphasic depuration was observed with an initial rapid phase that lasted several hr. Approximately 10% of accumulated 14C was associated with exoskeleton. As much as 50% of the accumulated B(a)P was transformed into polar compounds after one hr. Based on steady state 14C concentration, an apparent bioconcentration factor of 650 was determined. The bioconcentration value based on B(a)P analysis was 200.
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