Research and control of well water pollution in high esophageal cancer areas

Table 1 Three nitrogenous compounds pollution (mg/L) of the well water in Cixian County and Chichen County from 1993 to 1996

	Numbers of well	1993	1994	1995	1996
Nitrate nitrogen
Cixian	33	8.770b	13.381b	14.473b	19.554b
Chichen	31	3.829	4.452	4.351	8.022
Ratio		2.29	3.00	3.33	2.44
(Cixian/Chichen)
Nitrite nitrogen
Cixian	33	0.0144b	0.0629b	0.0407b	0.0101b
Chichen	31	0.0039	0.0094	0.0085	0.0020
Ratio		3.69	6.69	4.79	5.05
(Cixian/Chichen)
Ammonia nitrogen
Cixian	33	0.0094 b	0.0256b	0.0237	0.0117b
Chichen	31	0.0039	0.0029	0.0230	0.0028
Ratio		2.41	8.82	1.03	4.18
(Cixian/Chichen)

^bP < 0.01, There was a significant difference between two counties.