The Quality of Our Nation's Waters
Pesticides in the Nation's Streams and Ground Water, 1992-2001

Appendix 2 - Properties affecting the transport and fate of selected pesticide compounds.

[Pesticide compounds selected are those detected most frequently in NAWQA samples (see figs. 4-2 and 4-4), as well as several that were detected infrequently, despite extensive use. All values measured at (or estimated for) 25°C, except for those shown in italics. Unless noted otherwise, (1) values for octanol-water partition coefficient (K_ow, dimensionless), soil organic carbon-water partition coefficient (K_oc), water solubility (S_w) and Henry's law constant (K_H) are from Mackay and others (1997); (2) transformation half-lives in soil and water were measured in the laboratory (rather than in the field) at neutral pH in the dark, and obtained from the U.S. Department of Agriculture (2005); and (3) all are recommended values selected by the compilation authors when more than one value was available from the literature. Compounds are listed in the same order as in figures 4-2 and 4-4. Numbers of significant figures are identical to those given in original sources. kJ/mol, kilojoule per mole; mg/L, milligram per liter; mL/g, milliliter per gram; NA, data not available from any of the references consulted; Pa•m³/mol, pascal-cubic meter per mole; >, greater than.]

Compound	log Kow	log Koc (Koc in mL/g)	Sw (mg/L)	log KH (KH in Pa•m3/mol)	Half-life for transformation (days)
					In aerobic soil	In water
Agricultural herbicides and degradates detected most frequently in water
Atrazine	2.75	2.00	30	-3.54	146	1742
Deethylatrazine (DEA)	21.3	31.90	42700	5-4.12	6170	NA
Metolachlor	3.13	2.26	430	-2.63	26	7410
Cyanazine	2.22	2.3	171	-6.52	817	9>200
Alachlor	2.8	2.23	240	-2.7	1020.4	11640
Acetochlor	123.0	132.38	12,14223	12,15-2.15	13,1514	162300
Metribuzin	14,171.60	1.72	14,171,000	17,18-5.31	172	9>200
Bentazon	192.80	201.54	14,17500	21-3.7	2235	23>200
EPTC	3.2	2.3	370	0.00988	247	9>200
Trifluralin	5.34	4.14	250.5	1.00	169	26>32
Molinate	3.21	1.92	970	-0.839	2721	9>200
Norflurazon	172.45	172.55	1734	17-4.46	130	9>200
Urban herbicides detected most frequently in water
Simazine	2.18	2.11	5	-3.46	891	28>32
Prometon	2.99	2.54	750	-4.05	932	9>200
Tebuthiuron	81.79	172.1	292400	17-4.88	1050	30>2700
2,4-D	2.81	171.68	890	-3.61	312.3	7732
Diuron	2.78	2.6	40	-3.17	372	>500
Dacthal (DCPA)	324.28	173.75	170.5	17-0.66	3316	9>200
Bromacil	2.11	1.86	815	-4.89	275	34>30
Insecticides detected most frequently in water
Diazinon	3.3	2.76	60	-1.39	39	140
Chlorpyrifos	4.92	3.78	0.73	0.0374	30.5	29
Carbofuran	2.32	2.02	351	-4.30	11	35289
Carbaryl	2.36	2.36	120	-4.35	17	11
Malathion	2.8	3.26	145	-2.64	<1	366.3
Dieldrin37	5.20	4.08	0.17	0.0492	NA	3830
Organochlorine pesticide compounds detected most frequently in bed sediment and fish tissue
p,p'-DDE	5.7	5.0	0.04	0.900	NA	38>44,000
p,p'-DDD	5.5	5.0	0.05	-0.194	NA	3910,000
p,p'-DDT	6.19	5.4	0.0055	0.37	NA	405000
o,p'-DDE	5.8	85.58	0.1	0.405	NA	NA
o,p'-DDD	6.0	85.36	250.10	41-2.7	NA	39NA
o,p'-DDT	42NA	42NA	0.026	-0.460	NA	NA
cis-Chlordane	6.0	5.5	0.056	-0.466	NA	43>7.2x107
trans-Chlordane	6.0	5.5	0.056	-0.582	NA	44>10,000
Nonachlor	455.66	454.86	450.06	45-1.69	NA	NA
Oxychlordane	462.6	462.48	46200	46-1.52	NA	NA
Dieldrin37	5.20	4.08	0.17	0.0492	NA	3830
Heptachlor epoxide	5.0	4.0	0.35	460.51	NA	NA
Pentachloroanisole	465.66	464.62	460.2	462.91	NA	NA
Hexachlorobenzene	325.31	174.7	320.0062	471.69	NA	48>26,000
Chlorothalonil	2.64	3.2	0.6	1.77	NA	9>200
Dicamba	2.21	171.11	4500	-3.66	4928	9>200
Parathion-methyl (Methyl parathion)	3.0	3.7	25	-1.68	503.3	41
Pendimethalin	175.2	174.13	170.275	170.0899	1300	9>200
Terbufos	4.48	2.70	5	0.39	5	1.9

¹Measured by Khan (1978) in a solution containing 0.5 g/L fulvic acid.

²Computed from K_oc value using K_ow-vs.-K_oc regression for "triazines" from Sabljić and others (1995).

³K_oc value measured on a clay loam soil (1.3% organic carbon) by Seybold and Mersie (1996), the study—among those having measured K_oc for both DEA and atrazine—reporting the K_oc value for atrazine (140 mL/g) that was closest to the value selected for atrazine (100 mL/g) by Mackay and others (1997).

⁴Value from Ciba-Geigy, Ltd., cited by Bayless (2001)

⁵Estimated by (1) computing estimates of K_H for both DEA and atrazine (K_H,est[DEA] and K_H,est[atr], respectively) using the bond-contribution method of Meylan and Howard (1991); and (2) scaling from the value measured for atrazine (K_H,meas[atr]) using the following equation:

⁶Measured by Kruger and others (1997) in the aerobic soil (sandy clay loam, 0.6% organic carbon) for which the half-life for atrazine reported by the authors and adjusted to 25°C (191 d) was most similar to the value selected by the U.S. Department of Agriculture (2005) for atrazine at 25°C (146 d). Half-lives for both atrazine and DEA in soil were adjusted to 25°C from 24°C using an activation energy of 48.4 kJ/mol, measured by Baer and Calvet (1999) for atrazine disappearance in an aerobic silt loam (1.1% organic carbon).

⁷Rate extrapolated to 25°C using data reported by Cavalier and others (1991) for disappearance of the pesticide in ground-water samples (pH = 7.4-7.6) at 15 and 22°C, based on the experiment with the highest initial pesticide concentration (and thus maximum analytical sensitivity).

⁸Sole value reported by the U.S. Department of Agriculture (2005) database authors, but not "selected."

⁹Classified as "stable" with respect to hydrolysis (U.S. Department of Agriculture, 2005), meaning that the compound exhibits "less than 10% reaction after 30 days at 25°C" (Cheryl Sutton, U.S. Environmental Protection Agency Office of Pesticide Programs, Environmental Fate and Effects Division, personal communication, 1/4/05).

¹⁰Half-life interpolated to 25°C from rates of alachlor disappearance from a sandy loam soil (0.7% organic carbon) at 10, 20 and 30°C reported by Zimdahl and Clark (1982).

¹¹Rate extrapolated to 25°C from data reported by Cavalier and others (1991) for alachlor disappearance in ground water (pH = 7.4-7.6) at 15 and 22°C, based on the experiment with the highest initial alachlor concentration (and thus maximum analytical sensitivity). Value consistent with half-life estimate of ">100 d" at 20°C in deionized water reported by Gan and others (2002).

¹²Source: U.S. Environmental Protection Agency (1994).

¹³Median value among those reported by U.S. Environmental Protection Agency (1994).

¹⁴Measured at 20°C.

¹⁵Temperature of measurement not given.

¹⁶Source: Zheng and Ye (2001), cited by Carlson (2003). Consistent with half-life of ">100 d" at 20°C in deionized water reported by Gan and others (2002).

¹⁷Source: U.S. Department of Agriculture (2005).

¹⁸Adjusted from value measured at 20°C to 25°C using equation provided by Mackay and others (2000), and an enthalpy of vaporization (ΔH_v) of 46.8 kJ/mol, based on K_H data from 197 compounds (Staudinger and Roberts, 2001).

¹⁹Source: Sabljić and others (1995). Form of molecule (salt vs. benzothiadiazine) not given.

²⁰Measured using the sodium salt of bentazon, rather than the benzothiadiazine form (U.S. Department of Agriculture, 2005).

²¹Computed from dimensionless value given by Tiktak (1999). Temperature of measurement not given, but similarity of value to that computed from vapor pressure and solubility (both obtained from EXTOXNET) suggests that it may have been 20°C.

²²Median value among 19 measurements of bentazon disappearance rates in a variety of soils (pH= 6.1-7.7) over a temperature range of 20-23°C (Huber and Otto, 1994; Thorstensen and Lode, 2001), after adjusting all values to 25°C using an activation energy of 90 kJ/mol for bentazon disappearance, measured for a sandy soil with 4.90% organic carbon (Tiktak, 1999).

²³Statement by Huber and Otto (1994) that "hydrolytically, bentazon is nearly stable...at pH...7" presumed to be equivalent to U.S. Environmental Protection Agency's definition of "stable" (see footnote 9), although temperature of measurement not given.

²⁴"[H]alf-life in moist loam soil at 21 to 27°C is approximately one week" (Mackay and others, 1997).

²⁵According to Mackay and others (1997), "the reported values for this quantity vary considerably [0.05 - 40 mg/L for trifluralin; 0.10 - 0.24 mg/L for o,p'-DDD]; whereas this selected value represents the best judgement of the authors...it may be subject to large error."

²⁶Computed from rate constant (maximum value) provided by U.S. Department of Agriculture (2005).

²⁷According to Mackay and others (1997), "half-life is approximately 3 weeks in moist loam soils at 21-27°C."

²⁸For biodegradation in pond water. Source: Tucker and Boyd (1981), cited by Mackay and others (1997).

²⁹Arithmetic mean of the two values reported by U.S. Department of Agriculture (2005), neither of which was "selected."

³⁰Estimated from assumption that "no hydrolysis in 64 days" at 51°C and pH 3, 6 and 9 (U.S. Department of Agriculture, 2005) implies less than 5% reaction. Extrapolated to 25°C using the minimum activation energy (E_a) for the transformation in soil of methabenzthiazuron (35.6 kJ/mol), the urea herbicide most similar in structure to tebuthiuron among those for which E_a values appear to be available (FOCUS, 1997). (No E_a values appear to be available for the disappearance of either methabenzthiazuron or tebuthiuron in water.)

³¹Average of values computed for two soils, based on data reported by Veeh and others (1996).

³²Source: Syracuse Research Corporation CHEMFATE Database.

³³Source: Wettasinghe and Tinsley (1993).

³⁴Transformation rate given for pH 5 and 9 only (U.S. Department of Agriculture, 2005).

³⁵Transformation rate measured at pH 6.2 (U.S. Department of Agriculture, 2005).

³⁶Value measured at pH 7, rather than the pH (5) at which the value recommended by the U.S. Department of Agriculture (2005) was measured.

³⁷Dieldrin is both an insecticide and a product of aldrin transformation (Nowell and others, 1999), and was one of the pesticide compounds detected most frequently in bed sediments, as well as in water.

³⁸Reaction rate measured in 5% acetonitrile solution, extrapolated to 27°C from higher temperatures, and interpolated to pH 5 by Wolfe and others (1977).

³⁹No distinction made between o,p' and p,p' isomers for this parameter by the U.S. Department of Agriculture (2005), but reported half-life was identical to that provided by Ellington and others (1987a) for p,p'-DDD, suggesting that the U.S. Department of Agriculture (2005) value was for the p,p' isomer only.

⁴⁰Reaction rate measured in 5% acetonitrile solution, extrapolated to 27°C from higher temperatures, and interpolated to pH 7 by Wolfe and others (1977).

⁴¹Source: Suntio and others (1988).

⁴²Available estimation methods appear inadequate for distinguishing between ortho and para isomers.

⁴³Source: Ellington and others (1987a).

⁴⁴Estimated from assumption that "zero degradation...during five days" at 85°C and pH 7 (Ellington and others, 1987b) implies less than 10% reaction (Ellington and others, 1988). Extrapolated to 25°C using the activation energy for the transformation of γ-HCH in borate buffer at pH 9 (84.6 kJ/mol), reported by Ngabe and others (1993).

⁴⁵Source: Nowell and others (1999). No distinction made between cis and trans isomers.

⁴⁶Source: Nowell and others (1999).

⁴⁷Computed for 25°C using regression equation from Staudinger and Roberts (2001).

⁴⁸Estimated from assumption that "zero hydrolysis observed after 13 days at 85°C and pH 7 (Ellington and others, 1987b) implies less than 10% reaction (Ellington and others, 1988). Extrapolated to 25°C using the activation energy for the transformation of γ-HCH in borate buffer at pH 9 (84.6 kJ/mol), reported by Ngabe and others (1993).

⁴⁹Interpolated to 25°C from data for a clay soil (1.5% organic matter) by Comfort and others (1992).

⁵⁰Extrapolated to 25°C from value measured at 30°C in a silt loam soil (organic carbon content not given) by Lichtenstein and Schulz (1964) after 12 days of reaction (the longest reaction period examined by the authors), using the activation energy (E_a) measured by Lartiges and Garrigues (1995) for methyl parathion disappearance in unfiltered river water at pH 7.3 (26 kJ/mol). (No E_a values appear to be available for methyl parathion disappearance from aerobic soil.)

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