The Leaching of Atrazine and Plant Species Sensitivity to Atrazine using Bioassays and Chemical Analyses

Atrazine, one of the most frequently applied herbicides in the world, is highly persistent, and likely to contaminate runoff and groundwater resources, determined by bioassay and chemical analyses. In the present research the two following experiments were conducted in Mazandaran Province, Iran. 1) The sensitivity of eight plant species (canola, soybean, ryegrass, wild oat, wheat, littleseed canarygrass, redroot pigweed, and corn) to atrazine residues in the laboratory of the Qaemshahr Campus of the Islamic Azad University in 2019 was determined. Bioassay and GR₅₀ index were used to differentiate species. 2) The leaching front of atrazine in the laboratory of Mazandaran University of Medical Sciences was determined. Soil samples were collected from a 10-hectare-farm of Baykola Agricultural Research Station. The method of undisturbed soil columns was used to study atrazine leaching at three levels including control, usual dose (1.25 kg. ha⁻¹), and high dose (2.5 kg. ha⁻¹). The treatments were injected into soil columns inside 32-cm-high PVC pipes and after three days, 2-cm segments of the soil columns were exposed to bioassay and chemical analyses, simultaneously. In the first experiment, plants response to atrazine residues were different. Canola and corn were the most susceptible and tolerant crop species, respectively. The tolerance of other plant species to total residue, using GR₅₀ index, was according to the following order: canola < soybean < ryegrass < wild oat < wheat < littleseed canarygrass < redroot pigweed < corn. According to the bioassay test, at the high dose of atrazine, all traits were negatively affected, and the root weight and the ratio of root to shoot weight had the highest and the lowest decrease (28% and 12% relative to control), respectively. The simultaneous investigation of canola seedling weight and atrazine concentration, at different soil depths, revealed that atrazine penetrated to the 10-cm depth, which is attributed to higher organic matter and clay content. Canola was identified as a suitable plant for atrazine bioassay. Due to the depths of weed seed distribution and leaching front of atrazine in this experiment (on average, 10 cm), the contamination of weed seed lot with herbicides can be high.