Table 7.

Time dependence of esterase activity in various matrices^a

					Interstitial water
Time (h)	Bufferb	Waterc	Municipal effluent	Sacramento River water	Santa Mariad	Orcutt Creeke	Seawater
0	100 ± 12	89 ± 14	86 ± 21	132 ± 17	73 ± 10	83 ± 6	76 ± 18
1	103 ± 14	99 ± 20	78 ± 8	118 ± 1	65 ± 15	89 ± 4	90 ± 11
2	101 ± 18	101 ± 5	76 ± 11	108 ± 13	63 ± 21	82 ± 7	80 ± 6
4	102 ± 15	98 ± 6	71 ± 6	109 ± 13	49 ± 14	78 ± 4	78 ± 6
6	101 ± 21	93 ± 8	73 ± 7	116 ± 17	47 ± 17	76 ± 6	77 ± 7
8	94 ± 15	90 ± 4	61 ± 7	108 ± 14	36 ± 15	65 ± 7	70 ± 14
12	98 ± 16	94 ± 4	7 ± 4	96 ± 13	NDf	57 ± 5	59 ± 14
24	76 ± 18	74 ± 10	ND	3 ± 2	ND	ND	32 ± 11
36	77 ± 15	75 ± 7	ND	ND	ND	ND	11 ± 4
48	76 ± 12	71 ± 5	ND	ND	ND	ND	ND

^aAll values are shown as the percentage of activity relative to initial buffer control (100 mM, pH 7.4, phosphate buffer) and are the average of three replicates ± standard deviation. Enzyme (0.1 μg/ml, 18.4 mU/ml) was incubated in each matrix at 25°C, and activity was measured using the substrate p-nitrophenyl acetate. 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). Sources of all water samples are described in Materials and Methods.

^bSodium phosphate buffer (100 mM, pH 7.4).

^cMilli-Q^® water (Millipore, Billerica, MA, USA).

^dCollected from the Santa Maria River near Guadalupe (CA, USA).

^eCollected from Orcutt Creek near Guadalupe (CA, USA).

^fND = not detected.