Total trihalomethanes (TTHMs)

City of Pearland

Trihalomethanes are cancer-causing contaminants that form during water treatment with chlorine and other disinfectants. The total trihalomethanes group includes four chemicals: chloroform, bromodichloromethane, dibromochloromethane and bromoform. Read More.

Studies conducted in the U.S. and Europe have found that drinking tap water that carries disinfection byproducts increases the risk of developing bladder cancer. In animal studies, all trihalomethanes cause liver, kidney and intestinal tumors. Some human epidemiological studies also reported an association between disinfection byproducts and an increased risk of problems during pregnancy, including spontaneous miscarriage, cardiovascular defects, neural tube defects and low birth weight.

The health guideline of 0.15 parts per billion, or ppb, for the group of four trihalomethanes, or THM4/TTHM, was defined in a peer-reviewed scientific study by EWG and represents a one-in-one-million lifetime cancer risk level.

Click here to read more about disinfection byproducts.

MORE ABOUT THIS CONTAMINANT

192

Samples

Samples exceeding legal limit (MCL)

110

Samples exceeding
health guidelines

Testing results - average by year

Year	Average result	Samples taken	Detections	Range of results
2014	14.4 ppb	32	18	ND - 45.8 ppb
2015	19.2 ppb	32	18	ND - 49.3 ppb
2016	16.5 ppb	32	22	ND - 40.4 ppb
2017	12.4 ppb	32	16	ND - 41.1 ppb
2018	13.9 ppb	32	16	ND - 49.8 ppb
2019	16.5 ppb	32	20	ND - 45.9 ppb

ppb = parts per billion

State and national drinking water standards and health guidelines

EWG Health Guideline 0.15 ppb

EPA Maximum Contaminant
Level (MCL) 80 ppb

The legal limit for the group of four trihalomethanes, established in 1998, was based on the need for residual disinfectant levels in water served to customers and the cost of treatment. This limit does not fully protect against the risk of cancer due to exposure to trihalomethanes.

ppb = parts per billion

All test results

Date	Lab ID	Result
2014-02-21	AC44260	ND
2014-02-21	AC44256	29.4 ppb
2014-02-21	AC44261	ND
2014-02-21	AC44262	23.6 ppb
2014-02-21	AC44257	25.6 ppb
2014-02-21	AC44229	ND
2014-02-21	AC44259	24.8 ppb
2014-02-21	AC44258	22.5 ppb
2014-04-02	AC49099	ND
2014-04-02	AC49118	29.5 ppb
2014-04-02	AC49102	17.2 ppb
2014-04-02	AC49120	9.80 ppb
2014-04-02	AC49098	27.3 ppb
2014-04-02	AC49100	ND
2014-04-02	AC49101	28.6 ppb
2014-04-02	AC49097	30.8 ppb
2014-07-01	AC58602	ND
2014-07-01	AC58606	45.8 ppb
2014-07-01	AC58618	ND
2014-07-01	AC58597	ND
2014-07-01	AC58598	ND
2014-07-01	AC58605	ND
2014-07-01	AC58630	22.0 ppb
2014-07-01	AC58603	ND
2014-11-19	AC72450	15.2 ppb
2014-11-19	AC72475	33.1 ppb
2014-11-19	AC72448	ND
2014-11-19	AC72474	13.4 ppb
2014-11-19	AC72473	ND
2014-11-19	AC72449	ND
2014-11-19	AC72451	31.9 ppb
2014-11-19	AC72447	31.3 ppb
2015-02-25	AC82068	ND
2015-02-25	AC82087	36.3 ppb
2015-02-25	AC82066	ND
2015-02-25	AC82076	23.0 ppb
2015-02-25	AC82071	21.8 ppb
2015-02-25	AC82070	ND
2015-02-25	AC82069	23.2 ppb
2015-02-25	AC82067	23.3 ppb
2015-04-14	AC88088	ND
2015-04-14	AC88092	36.6 ppb
2015-04-14	AC88094	ND
2015-04-14	AC88095	30.3 ppb
2015-04-14	AC88089	38.1 ppb
2015-04-14	AC88091	ND
2015-04-14	AC88084	47.4 ppb
2015-04-14	AC88090	40.5 ppb
2015-07-13	AC99064	ND
2015-07-13	AC99101	49.3 ppb
2015-07-13	AC99065	ND
2015-07-13	AC99062	ND
2015-07-13	AC99061	ND
2015-07-13	AC99063	ND
2015-07-13	AC99102	47.5 ppb
2015-07-13	AC99094	43.9 ppb
2015-11-06	AD12958	18.2 ppb
2015-11-06	AD12947	33.9 ppb
2015-11-06	AD12948	ND
2015-11-06	AD12930	ND
2015-11-06	AD12949	ND
2015-11-06	AD12957	20.1 ppb
2015-11-06	AD12950	41.8 ppb
2015-11-06	AD12952	40.1 ppb
2016-03-08	AD27528	ND
2016-03-08	AD27532	24.6 ppb
2016-03-08	AD27529	5.80 ppb
2016-03-08	AD27533	15.5 ppb
2016-03-08	AD27530	ND
2016-03-08	AD27527	32.9 ppb
2016-03-08	AD27525	32.2 ppb
2016-03-16	AD29021	ND
2016-05-25	AD38243	ND
2016-05-25	AD38237	40.4 ppb
2016-05-25	AD38221	ND
2016-05-25	AD38238	40.4 ppb
2016-05-25	AD38218	40.2 ppb
2016-05-25	AD38266	ND
2016-05-25	AD38222	39.9 ppb
2016-05-25	AD38239	17.6 ppb
2016-09-29	AD51887	ND
2016-09-29	AD51892	25.2 ppb
2016-09-29	AD51891	ND
2016-09-29	AD51885	10.4 ppb
2016-09-29	AD51884	4.90 ppb
2016-09-29	AD51886	29.3 ppb
2016-09-29	AD51889	25.0 ppb
2016-09-29	AD51888	26.4 ppb
2016-10-21	AD54281	ND
2016-10-21	AD54282	15.3 ppb
2016-10-21	AD54297	ND
2016-10-21	AD54289	20.3 ppb
2016-10-21	AD54290	15.1 ppb
2016-10-21	AD54296	22.0 ppb
2016-10-21	AD54298	23.2 ppb
2016-10-21	AD54295	22.5 ppb
2017-01-17	AD65070	ND
2017-01-17	AD65076	21.0 ppb
2017-01-17	AD65077	ND
2017-01-17	AD65066	21.1 ppb
2017-01-17	AD65071	15.0 ppb
2017-01-17	AD65075	ND
2017-01-17	AD65069	22.7 ppb
2017-01-17	AD65072	21.1 ppb
2017-04-12	AD79421	36.4 ppb
2017-04-12	AD79427	ND
2017-04-12	AD79422	ND
2017-04-12	AD79424	ND
2017-04-12	AD79426	35.6 ppb
2017-04-12	AD79425	ND
2017-04-12	AD79423	39.6 ppb
2017-04-12	AD79428	36.5 ppb
2017-07-18	AD89677	ND
2017-07-18	AD89683	5.90 ppb
2017-07-18	AD89681	ND
2017-07-18	AD89678	ND
2017-07-18	AD89679	ND
2017-07-18	AD89684	ND
2017-07-18	AD89682	1.10 ppb
2017-07-18	AD89680	ND
2017-10-18	AE01318	5.70 ppb
2017-10-18	AE01319	41.1 ppb
2017-10-18	AE01315	29.0 ppb
2017-10-18	AE01323	ND
2017-10-18	AE01322	ND
2017-10-18	AE01320	ND
2017-10-18	AE01317	30.8 ppb
2017-10-18	AE01314	33.5 ppb
2018-03-07	AE17247	1.10 ppb
2018-03-07	AE17257	49.8 ppb
2018-03-07	AE17255	ND
2018-03-07	AE17246	ND
2018-03-07	AE17245	ND
2018-03-07	AE17256	ND
2018-03-07	AE17239	ND
2018-03-07	AE17244	ND
2018-04-03	AE20985	ND
2018-04-03	AE20982	25.8 ppb
2018-04-03	AE20980	ND
2018-04-03	AE20984	ND
2018-04-03	AE20986	ND
2018-04-03	AE20981	ND
2018-04-03	AE20983	27.4 ppb
2018-04-03	AE20979	26.1 ppb
2018-08-13	AE36618	ND
2018-08-13	AE36600	32.1 ppb
2018-08-13	AE36602	5.10 ppb
2018-08-13	AE36612	1.20 ppb
2018-08-13	AE36608	6.10 ppb
2018-08-13	AE36601	ND
2018-08-13	AE36609	31.9 ppb
2018-08-13	AE36610	34.2 ppb
2018-10-18	AE43902	ND
2018-10-18	AE43908	39.8 ppb
2018-10-18	AE43909	ND
2018-10-18	AE43907	38.7 ppb
2018-10-18	AE43906	40.1 ppb
2018-10-18	AE43903	ND
2018-10-18	AE43904	42.7 ppb
2018-10-18	AE43905	41.8 ppb
2019-01-29	AE51881	ND
2019-01-29	AE51883	24.7 ppb
2019-01-29	AE51892	ND
2019-01-29	AE51876	25.7 ppb
2019-01-29	AE51880	25.6 ppb
2019-01-29	AE51889	ND
2019-01-29	AE51890	27.3 ppb
2019-01-29	AE51882	26.6 ppb
2019-04-23	AE63341	ND
2019-04-23	AE63369	32.2 ppb
2019-04-23	AE63366	ND
2019-04-23	AE63348	15.0 ppb
2019-04-23	AE63343	27.9 ppb
2019-04-23	AE63344	ND
2019-04-23	AE63342	39.7 ppb
2019-04-23	AE63370	32.6 ppb
2019-07-02	AE73077	22.8 ppb
2019-07-02	AE73067	1.90 ppb
2019-07-02	AE73068	5.00 ppb
2019-07-02	AE73102	ND
2019-07-02	AE73073	21.0 ppb
2019-07-02	AE73075	42.6 ppb
2019-07-02	AE73076	38.9 ppb
2019-07-10	AE73891	ND
2019-10-14	AE86458	ND
2019-10-14	AE86460	28.4 ppb
2019-10-14	AE86459	1.000 ppb
2019-10-14	AE86461	ND
2019-10-14	AE86462	ND
2019-10-14	AE86468	ND
2019-10-14	AE86465	45.9 ppb
2019-10-14	AE86442	43.9 ppb