These tests measure organic chemicals in drinking water: disinfection by-products, volatile organic compounds, pesticides and herbicides, and PFAS. Each test below names the EPA method and how it works. Results are reported in micrograms per liter (µg/L), or nanograms per liter (ng/L) for PFAS. Total organic carbon is described with the wastewater and environmental chemistry tests.
| Test | Method |
|---|---|
| Trihalomethanes (THM) | EPA Method 524.2 |
| Haloacetic acids (HAA) | EPA Method 552.2 |
| Disinfection by-product formation potential | No method number listed |
| Volatile organic compounds (VOC) | EPA Methods 524.2 and 524.3 |
| Synthetic organic compounds (SOC) | EPA Methods 525.2, 531.1 and 515.3 |
| Pesticides and insecticides | EPA Method 525.2; EPA Method 505 |
| Compounds in the pesticide and SOC tests | EPA Method 525.2; EPA Method 505 |
| Chlorinated acid herbicides | EPA Method 515.3 |
| Carbamates | EPA Method 531.1 |
| Glyphosate | EPA Method 547 |
| PFAS (per- and polyfluoroalkyl substances) | EPA Method 533 |
| Acrylamide and epichlorohydrin | No method number listed |
| DBCP and ethylene dibromide (EDB) | No method number listed |
| Diquat | No method number listed |
| Endothall | No method number listed |
| Dioxin (2,3,7,8-TCDD) | No method number listed |
Disinfection by-products
EPA Method 524.2, purge and trap gas chromatography/mass spectrometry (GC/MS): an inert gas is bubbled through the sample, the volatile compounds are caught on a trap, then released into the gas chromatograph and identified and measured by their mass spectra. The four trihalomethanes (chloroform, bromodichloromethane, dibromochloromethane and bromoform) are reported individually and as total trihalomethanes, in µg/L.
EPA Method 552.2: the acids are extracted from the acidified sample into methyl tert-butyl ether, converted to their methyl esters with acidic methanol, and measured by gas chromatography with an electron capture detector. Results are reported for the individual acids and as the regulated total of five (HAA5), in µg/L.
Formation potential shows how much trihalomethane and haloacetic acid a water can form when it is chlorinated: the sample is dosed with chlorine and held for a set time, then the by-products formed are measured. The result reflects the natural organic matter in the water and is used to compare source waters and plan treatment. It is a different measurement from the by-products already present in treated water.
Volatile organic compounds
EPA Methods 524.2 and 524.3, purge and trap GC/MS, the same technique as the trihalomethane test. The regulated drinking-water volatile compounds, such as benzene, trichloroethylene, tetrachloroethylene and vinyl chloride, are identified by their mass spectra and reported in µg/L. EPA 524.3 is the newer revision of the method.
Pesticides and herbicides
The drinking-water SOC group combines EPA Methods 525.2, 531.1 and 515.3, described below. Each part can also be ordered on its own, as can glyphosate.
EPA Method 525.2: organic compounds are extracted from the sample on a solid phase sorbent, washed off with solvent, and identified and measured by GC/MS. EPA Method 505: chlorinated pesticides and PCBs (as Aroclors) are extracted into a small volume of hexane and measured by gas chromatography with an electron capture detector. Reported in µg/L.
The pesticide and insecticide test above (EPA Methods 525.2 and 505) covers the regulated drinking-water compounds named in the public water system list. The pesticides are the herbicides alachlor, atrazine and simazine and the insecticides chlordane, endrin, heptachlor, lindane, methoxychlor and toxaphene, with heptachlor epoxide, a breakdown product of heptachlor. The others are not pesticides: benzo(a)pyrene, a polycyclic aromatic hydrocarbon; the plasticizers di(2-ethylhexyl) adipate and di(2-ethylhexyl) phthalate; hexachlorobenzene and hexachlorocyclopentadiene, chlorinated industrial chemicals; and polychlorinated biphenyls (PCBs), measured as Aroclor mixtures. All of these compounds are on the analyte list of EPA Method 525.2; EPA Method 505 measures chlorinated pesticides and PCBs by gas chromatography with an electron capture detector. Results are given in µg/L for each compound; PCBs are reported as Aroclor mixtures rather than as single compounds.
EPA Method 515.3: acid herbicides such as 2,4-D, dalapon and pentachlorophenol are extracted from the acidified sample, converted to their methyl esters, and measured by gas chromatography with an electron capture detector. Reported in µg/L.
EPA Method 531.1: N-methylcarbamates and N-methylcarbamoyloximes, such as aldicarb, carbofuran and oxamyl, are separated by high-performance liquid chromatography (HPLC). After the column they are broken down with sodium hydroxide, and the methylamine released reacts with o-phthalaldehyde to give a fluorescent product that is measured. Reported in µg/L.
EPA Method 547: glyphosate is separated by HPLC and oxidized after the column to glycine, which reacts with o-phthalaldehyde to give a fluorescent product that is measured. Reported in µg/L.
PFAS
EPA Method 533: the PFAS are concentrated from the sample on a weak anion exchange solid phase extraction cartridge and measured by liquid chromatography with tandem mass spectrometry (LC-MS/MS), with isotope-labeled standards added to each sample for quantitation (isotope dilution). The PFAS listed in the method, including PFOA and PFOS, are reported in ng/L. The method is for drinking water.
Other regulated organic chemicals
Both are monomers that can remain in water treatment chemicals: acrylamide in polyacrylamide coagulant aids, and epichlorohydrin as an impurity of some treatment chemicals. EPA regulates them by treatment technique rather than by a maximum contaminant level: each water system certifies to the state that the dose of the treatment chemical combined with its monomer level stays within set limits (acrylamide 0.05% dosed at 1 mg/L; epichlorohydrin 0.01% dosed at 20 mg/L). Contact us before sampling if you need either compound measured in water.
1,2-Dibromo-3-chloropropane (DBCP) is a former soil fumigant, and EPA lists runoff and leaching from its use as the source in drinking water; EPA lists discharge from petroleum refineries as the source of ethylene dibromide. Both are regulated at very low levels: the EPA maximum contaminant levels are 0.0002 mg/L for DBCP and 0.00005 mg/L for EDB. Concentrations this low are usually expressed in µg/L.
Diquat is a herbicide used on crops and aquatic weeds. EPA lists runoff from herbicide use as its source in drinking water and sets a maximum contaminant level of 0.02 mg/L. Concentrations are usually expressed in µg/L.
Endothall is a herbicide, used mainly to control aquatic weeds. EPA lists runoff from herbicide use as its source in drinking water and sets a maximum contaminant level of 0.1 mg/L. Concentrations are usually expressed in µg/L.
2,3,7,8-Tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) is the dioxin regulated in drinking water. EPA lists emissions from waste incineration and other combustion and discharge from chemical factories as its sources, and sets a maximum contaminant level of 0.00000003 mg/L (30 picograms per liter), one of the lowest for any regulated contaminant, so concentrations are usually expressed in pg/L.
Organic samples are collected in the containers each method specifies. Contact us for sampling instructions before you collect the sample.
The method numbers on this page follow the published EPA and Standard Methods designations. These references describe the methods; the TNI LAMS registry lists each method’s code and revision.
Questions about a sample or a method, call 360-967-7010 or email [email protected].
