Effect of Temperature and Moisture on Degradation of Herbicide Atrazine in Agricultural Soil

Modern agricultural practices often require extensive use of herbicides for production of corn, soybeans, sorghum, and other row crops. Due to the continuous use of herbicides in agriculture, appreciable quantities of herbicides and their degraded products may accumulate in the ecosystem leading to serious problem to man and the environment. Herbicides, which enter the soil environment, are subject to a variety of degradation processes. The overall degradation of a pesticide from soil results from a combination of mechanisms such as microbial degradation, chemical hydrolysis, photolysis, volatility, leaching and surface runoff. The degree to which each mechanism will contribute to the overall degradation of the pesticide is in turn dependent on the physicochemical properties of the pesticide, characteristics of the soil, environmental conditions and management practices.1 Therefore, it is essential to study the residue and degradation pattern of herbicides in soil, crops and water systematically in order to generate meaningful data from the point of view of plant protection, public health and environmental safety. 

Atrazine is one of the most widely used herbicides all over the world. It is a pollutant of environmental concern due to its low biodegradability and its high potential to contaminate the surface waters and ground water. Several epidemiological cancer studies concerning atrazine and its possible association with carcinogenic effects in humans are being reviewed by the US EPA.2 The acute toxicity of atrazine’s metabolites such as deethyl- and deisopropylatrazine was found to be twice as that of atrazine.3 Although several countries gave up the use of atrazine because of its toxicity, it is still one of the most popular herbicide in many countries.4 Therefore, the development of ecological farming is encouraged. 

The factors influencing the degradation of pesticides in soil were reviewed.1) An updated overview of atrazine degradation by microorganisms under different ecosystems was presented.5 Some microbial consortia were reported for their metabolic cooperative actions by investigating the individual’s contribution in atrazine degradation.6,7 The degradation of atrazine in plant and water was reported by using biotic or abiotic method.8-10 Biodegradation of atrazine in different soils using various bioprocessed material were investigated.11 The best studied atrazine-degrading bacterium is Pseudomonas sp. strain ADP which was isolated from a herbicide spill site.12 Dependence of accelerated degradation of atrazine on soil pH in French and Canadian soils was investigated, where both hydroxylated and dealkylated atrazine metabolites were detected, but no clear pattern of metabolite production could be determined.13 Different environmental conditions obviously influence on the degradation of atrazine. The effects of temperature and moisture on the soil net nitrogen mineralization was investigated based on N content change,14 but without degradation information before mineralization process. The degradation rates of atrazine in the control soil at three temperatures were measured by quantification with high performance liquid chromatography (HPLC).15 This study showed that its degradation was faster in the unsterilized soil than in sterilized soil and illustrated that microbial degradation contributed to the overall degradation, but without any information for the degraded products.  

Currently, no information is available concerning the combined effect of temperature and moisture on the degradation rate and its degraded products of atrazine in agricultural soil. The primary objective of this study was to assess simultaneously the effects of temperature and moisture upon atrazine degradation in loam soil with an ultra-performance liquid chromatography–electrospray ionization–mass spectrometry (UPLC‒ESI‒MS). This information will be useful in understanding the behavior of atrazine in soil in a temperature- and moisture-controlled environment, and in selecting the conditions needed for achieving optimal degradation, as well as in evaluating the potential impact of its degraded products.