Atrazine transport from the maize (Zea mays L.) cultivated upland soil in Huay Kapo Watershed, Nam Nao District, Phetchabun Province, Thailand.

摘要

Huay Kapo Watershed is located in Lakdan Sub-District, Nam Nao District, Phetchabun Province, Thailand. The watershed is located at approximately 400-920 m MSL, has a slope of approximately 18%, high erodibility, and a high soil loss rate (120.15 t ha-1 yr-1). This area is used to cultivate maize (Zea mays L.) year round and receives atrazine at a rate 1.25-1.56 kg ha-1. Topsoil (0-15 cm), subsoil (15-30 cm), soil sediment and stream water were collected from 15 stations during the rainy season (August-November 2008). The analytical results revealed that topsoil and subsoil of the upland soils were mostly sandy clay loam, with pH 5.0, low CEC (average 13.30 and 9.75 cmol kg-1, respectively), low clay content (23.60 and 25.10%, respectively) and low organic matter (1.78 and 1.45%, respectively). Topsoil at the amount of 80% of the total 48 samples contained atrazine, with the 133.59 micro g kg-1 average concentration, while 83.33% of the total 50 samples of subsoil was contaminated with atrazine at the average concentration of 183.23 micro g kg-1. Furthermore, 71.76% of the sediment samples were found to contain atrazine at the average concentration of 27.42 micro g kg-1. The soil sediment samples were mostly sand and had a low clay content (4.02%), low organic matter (0.45%), low CEC (4.36 cmolkg-1) and pH of 6.5. Stream water samples at the amount of 63.33% of all samples were contaminated with atrazine from the cultivated area with the average atrazine concentration of 4.7 micro g L-1. The stream water as many as 15 samples (39.47% of the total samples) contained atrazine in levels higher than the standard limit of atrazine concentration in drinking water set by USEPA at 3 micro g L-1. Atrazine in the upland soil was 4.87-fold higher than that in the soil sediment and 39- fold higher than that in the stream water. Additionally, the content of atrazine in the soil sediment was 5.87-fold higher than that in the stream water. Overall, the contents of atrazine could be ranked in the following order: subsoil > topsoil > soil sediment > stream water. The results revealed that atrazine was transported from upland soils into the aquatic environment by adsorption, run-off and leaching processes.