Kinetics and biotransformation of benzo(a)pyrene in Chironomus riparius.

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.

Use of a fractional factorial design to evaluate interactions of environmental factors affecting biodegradation rates.

For investigation of main and interactive effects of six experimentally controlled environmental factors on phenol biodegradation in a shake-flask system, a largely neglected statistical procedure was applied. A major benefit resulting from the application of the orthogonal, fractional factorial design is that the number of experiments necessary to evaluate multifactor interactions is limited. In our investigation, the required number of experiments was reduced to 81 from the 324 necessary with conventional factorial designs; information was sacrificed for only 3 of 15 possible two-factor interactions. Six experimentally controlled factors were investigated at two or three treatment levels each; the six factors were (1) amount of phenol substrate, (2) amount of bacterial inoculum, (3) filtration of inoculum, (4) type of basal salts medium, (5) initial pH of basal salts medium, and (6) flask closure. Significant main effects were found for factors 1, 2, and 4; whereas significant interactive effects were found only for factor 2 with factor 3 and for factor 2 with factor 5. Our results suggest that the application of these statistical designs will greatly reduce the number of experiments necessary to evaluate multifactor effects on degradation rates during optimization of both hazard screening systems and waste treatment systems.