Fifteen insecticides, which were banned in Vietnam in the period from 1990 to 1998,
were chosen for the investigation of surface water samples in Hanoi and its surroundings.
The investigation was focused on an area of approximately 30 by 20 km. Thirty water
samples, in total were analysed: 11 samples from the Red river, seven from the Duong
river, four from various lakes (West lake, Thuyen Quang, Bay Mau, Ba Mau), six from
irrigation canals and two samples from wells. The procedure was repeated in November
1998 and in August 1999. The results showed that the contamination of the banned pesticides
was highest in the rivers and then in the irrigation canals, followed by the lakes
and wells. These pesticides could hardly be determined in just two drinking water
samples (wells) and their concentrations rarely exceeded detection limits (0.05-0.25
ng l(-1)). The mean concentrations of sigmaHCHs (alpha, beta, gamma, delta-HCH) and
sigmaDDTs (2,4'-, 4,4'-DDE; 2,4'-, 4,4'-DDD; 2,4'-, 4,4'-DDT) in the rivers were 17.2
+/- 71.8 and 43.7 +/- 79.9 ng l(-1) in the dry season (DS, November 1998), 29.3 +/-
117 and 56.1 +/- 65.6 ng l(-1) in the rainy season (RS, August 1999), respectively.
However, the highest concentration of DDTs detected in a river sample (DS): 0.324
microg l(-1) was much lower than their allowable limit of concentration in surface
waters, which is accorded with Criteria of Vietnam (1995) (DDTs < 10 microg l(-1)).
Moreover, endrin, heptachlor, aldrin were also detected in most of water samples with
considerable mean concentrations in rivers: 25.3 +/- 40.5, 17.4 +/- 23.8, 11.0 +/-
9.02 ng l(-1) in the DS and 18.5 +/- 23.2, 19.3 +/- 29.0, 12.8 +/- 8.44 ng l(-1) in
the RS, respectively. Heptachlor epoxide (isomer A) and dieldrin were detected in
some water samples with lowest concentrations.