Table 6. Maximum concentration and detection frequency for all compounds detected. 


[Compounds are listed in descending order of frequency within each compound class. CAS Registry Number^® is a registered trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client Services^SM. Abbreviations: CAS, Chemical Abstracts Service; LRL, laboratory reporting level; µg/L, micrograms per liter]


Compound	CAS Registry number®	Number of samples collected	Number of samples with detections	Maximum detected concentration (µg/L)	Frequency of detections (percent)	Frequency based on common LRL (percent)
Fungicide
cis-Propiconazole 2	112721-87-6	42	3	0.051	7.1
trans-Propiconazole 2	120523-07-1	42	3	0.08	7.1
Herbicide
Hexazinone	51235-04-2	71	19	0.097	26.8
2,4-D 1,2	94-75-7	126	33	1.65	26.2	12.3
Atrazine 1,2	1912-24-9	134	29	0.053	21.6
Glyphosate 1	1071-83-6	68	14	0.43	20.6	11.2
Diuron 2	330-54-1	126	21	6.07	16.7	6.1
Prometon	1610-18-0	133	19	0.06	14.3
Sulfometuron-methyl	74222-97-2	126	18	1.61	14.3	2.5
Imazapyr	81334-34-1	52	7	0.209	13.5	1.8
Sum 2,4-D + 2,4-D ME 1,2	42	5	0.04	11.9
2,4-DB 2	94-82-6	125	14	0.1	11.2	0.6
Triclopyr	55335-06-3	126	13	3.1	10.3	3.1
Nicosulfuron	111991-09-4	126	7	0.13	5.6	0.6
Tebuthiuron	34014-18-1	134	6	3.47	4.5	2.2
Simazine 1,2	122-34-9	133	5	0.228	3.8	1.2
Bentazon	25057-89-0	126	4	0.03	3.2
Metolaclor 2	51218-45-2	133	4	0.01	3.0
Picloram 1,2	1918-02-1	126	3	1.86	2.4	1.8
Trifluralin 2	1582-09-8	133	3	0.002	2.3
Diphenamid	957-51-7	126	2	0.02	1.6
Fluometuron	2164-17-2	126	2	0.02	1.6
Metsulfuron methyl	74223-64-6	126	2	0.62	1.6	1.2
Dicamba	1918-00-9	126	1	0.58	0.8	0.6
Siduron	1982-49-6	126	1	0.16	0.8	0.6
Dinoseb 1	88-85-7	126	1	0.01	0.8
Alachlor 1,2	15972-60-8	133	1	0.009	0.8
Pronamide 2	23950-58-5	133	1	0.014	0.8
Insecticide
Carbaryl 2	63-25-2	133	35	1.3	26.3	2.2
Diazinon 2	333-41-5	133	18	0.115	13.5	0.6
Fipronil 2	120068-37-3	119	5	0.041	4.2
Malathion 2	121-75-5	133	3	0.04	2.3
HCH (gamma) Lindane 1,2	58-89-9	63	1	0.01	1.6
Imidacloprid	138261-41-3	126	2	0.159	1.6	0.6
Cypermethrin 2	52315-07-8	71	1	0.014	1.4
Propoxur	114-26-1	126	1	0.007	0.8
Chlorpyrifos 2	2921-88-2	133	1	0.01	0.8
Metabolite
AMPA	1066-51-9	68	21	0.95	30.9	3.8
CIAT	6190-65-4	134	21	0.013	15.7
OIET	2163-68-0	126	11	0.042	8.7
Desulfinylfipronil	119	9	0.006	7.6
1-Naphthol	90-15-3	71	1	0.01	1.4
Human waste indicator
Caffeine	58-08-2	126	40	11.4	31.7	13.5

¹Compounds regulated by drinking-water standards.

²Compounds known or suspected to be endocrine disruptors.

First posted May 30, 2012