. 2020 May 18;128(5):057006. doi: 10.1289/EHP6012

Table 2.

Area-specific characteristics by average total trihalomethane (TTHM) exposure (second and third trimester) and chlorination treatments for all births, expressed as proportions (%).

Variables^a	No chlorination	All			Chloramine			Hypochlorite
Variables^a	No chlorination	$< 5 μ g TTHM / L$	$5 - 15 μ g TTHM / L$	$> 15 μ g TTHM / L$	$< 5 μ g TTHM / L$	$5 - 15 μ g TTHM / L$	$> 15 μ g TTHM / L$	$< 5 μ g TTHM / L$	$5 - 15 μ g TTHM / L$	$> 15 μ g TTHM / L$
Second trimester
$n$	66,008	262,177	138,672	81,762	172,320	15,240	33,996	27,803	28,768	43,893
Average $μ g TTHM / L$	—	0.76	9.0	24	0.67	8.0	25	1.3	10	23
Water source
Surface water	5	87	83	57	97	99	80	17	25	41
Groundwater	95	13	17	43	3	0.0066	20	83	75	59
Chlorination treatment
Chloramine	0	86	17	45	100	100	100	—	—	—
Hypochlorite	0	15	25	55	—	—	—	100	100	100
Chlorine dioxide^b	0	1.8	60	0.18	—	—	—	—	—	—
Chlorine gas	0	0	1.6	0.0013	—	—	—	—	—	—
Population ( $n$ )
$< 20,000$	25	1.2	1.4	3.5	0.48	0	0	7.9	5.1	6.3
20,000–200,000	75	60	34	41	71	85	25	92	83	50
$> 200,000$	0	39	65	56	28	15	75	0	12	44
Third trimester
$n$	66,008	263,687	168,449	78,439	173,265	22,204	34,237	28,527	48,731	42,477
Average $μ g TTHM / L$	—	0.75	9.2	24	0.66	8.9	25	1.3	10	22
Water source
Surface water	5	97	80	56	97	96	74	18	38	40
Groundwater	95	13	20	44	3.2	4.5	26	83	62	60
Treatment
Chloramine	0	86	19	44	100	100	100	—	—	—
Hypochlorite	0	16	34	56	—	—	—	100	100	100
Chlorine dioxide^b	0	2.0	50	0.36	—	—	—	—	—	—
Chlorine gas	0	0.0011	1.5	0.010	—	—	—	—	—	—
Population ( $n$ )
$< 20,000$	25	1.2	2.8	3.5	0.49	0.0090	0	8.2	8.2	6.1
20,000–200,000	75	60	35	40	72	72	29	92	65	48
$> 200,000$	0	39	62	57	28	28	71	0	27	46

Note: —, not applicable; TTHM, total trihalomethanes.

^{^a}

No missing data.

^{^b}

Used in combination with chlorite or chlorite and chlorine gas.