Table 2.

Effect of liquid esterase on pyrethroid toxicity to Ceriodaphnia dubia^a

	48-h mortality (%)
	Active enzymec					Inactive enzymed		BSAe
Pyrethroid (ng/L)b	0xf	1x	5x	10x	100x	10x	100x	10x	100x
Permethrin
Laboratory waterg
0	0	0	0	0	0	11 ± 19	0	0	0
500	100	100	60 ± 28	0	0	100	65 ± 10	85 ± 30	90 ± 11
750	100	100	75 ± 10	0	0	100	100	100	100
1,000	100	100	70 ± 38	0	0	100	100	100	100
Sacramento River waterh
0	0	0	0	0	0	0	0	0	0
500	100	95 ± 10	0	0	0	100	60 ± 16	85 ± 10	85 ± 19
750	100	100	21 ± 28	0	0	100	100	100	100
1,000	100	100	75 ± 19	0	0	100	100	100	100
Bifenthrin
Laboratory waterg
0	0	0	0	0	0	0	0	0	0
300	100	100	0	0	5 ± 10	100	100	100	100
450	100	100	0	0	0	100	100	100	100
600	100	100	40 ± 43	0	0	100	100	100	100
Sacramento River waterh
0	5± 10	0	0	0	0	0	0	0	5 ± 10
300	100	100	46 ± 37	5 ± 10	0	100	100	100	100
450	100	100	95 ± 10	45 ± 33	5 ± 10	100	100	100	100
600	100	100	100	79 ± 17	0	100	100	100	100

^aData are the average of four replicates with five neonates ± standard deviation.

^bPyrethroid concentrations are nominal water concentrations.

^cEsterase was prepared as described in Materials and Methods.

^dEsterase was heated at 100°C for 4 min.

^eBovine serum albumin (BSA) was added at protein concentrations equivalent to those used in the esterase preparations.

^f1x dilution = 2.3 × 10⁻³ U/ml. A unit of activity is the amount of enzyme that hydrolyzes 1.0 μmol of butyrate to butyric acid and ethanol per minute at pH 8.0 at 25°C (as defined by Sigma Chemical, St. Louis, MO, USA).

^gWater amended to U.S. Environmental Protection Agency moderately hard specifications.

^hSacramento River water was collected at Garcia Bend, near Sacramento (CA, USA).