Abstract—Pesticides have been used widely over the world in agriculture to protect from pests and reduce crop losses. However, it affects the environment with toxic chemicals. Exceed of toxic constituents in the ecosystem will result in bad side effects. The hydrological cycle is related to the existence of pesticides and heavy metal which it can penetrate through varieties of sources into the soil or water bodies, especially runoff. Therefore, proper mechanisms of pesticide and heavy metal removal should be studied to improve the quality of ecosystem free or reduce from unwanted substances. This paper reviews the use of treatment train and its mechanisms to minimize pesticides and heavy metal from agricultural runoff. Organochlorine (OCL) is a common pesticide that was found in the agricultural runoff. OCL is one of the toxic chemicals that can disturb the ecosystem such as inhibiting plants' growth and harm human health by having symptoms as asthma, active cancer cell, vomit, diarrhea, etc. Thus, this unwanted contaminant gives disadvantages to the environment and needs treatment system. Hence, treatment train by bioretention system is suitable because removal efficiency achieves until 90% of pesticide removal with selected vegetated plant and additive. Keywords—Pesticides, heavy metal, agricultural runoff, bioretention, mechanism removal, treatment train. I. INTRODUCTION GRICULTURE has become one of the biggest industries that contribute to nation development. Many lands were explored to fulfill the aggressive needs to support the demand. Despite that, it results in the environment being polluted due to uncontrolled agriculture activities. The development of agricultural lands has led the pollution entering water bodies by agricultural runoff. This problem arises when most of the agriculture agencies use pesticides to control losses from crop yields devastation. Many farmers were interested in using pesticides rather than implementing organic plantation as it gives more profit and saves time to control pests. The usage of pesticides became widespread worldwide to maintain the high quality product fruits and vegetables [1]. Pesticides usage gives benefits to crop production as it increases the percentage production and reduces the crop Nor.Amirah Ahmad Zubairi is with the Universiti Teknologi Petronas, Bandar Sri Iskandar, 32610 Perak (corresponding author, phone: 011- 11636966; e-mail: nor_19001668@ utp.edu.my). Husna Takaijudin, is with Universiti Teknologi Petronas, Bandar Sri Iskandar, 32610 Perak. (e-mail: husna_takaijudin@utp.edu.my). Khamaruzaman Wan Yusof is with the Civil and Environmental Engineering Department, Universiti Teknologi Petronas, Bandar Sri Iskandar, 32610 Perak (e-mail: khamaruzaman.yusof@utp.edu.my). losses. However, it leads to pollution in the environment due to the chemical ingredients [2]. Those ingredients increased the toxicity towards the environment and affected human health. Farmers have high possibility of being affected by the toxicity of pesticide because of agricultural practices such as pesticide spray techniques. The techniques require the farmers to spray the pesticides towards crop. Once it was exposed into the air, some of the chemicals evaporated while farmers also indirectly inhale the air that mixes with unwanted chemicals. As the pesticides are commonly applied through spray techniques, chemical ingredients from pesticides are absorbed into soil and water bodies [3]. Then, the polluted water flows from the agricultural area and enters the swale that contaminates the soil and water. Nevertheless, this pollution could be not only pesticides but all pollutants that flow from the agricultural area such as sediments, nutrients or heavy metal mixing up together and flowing until final destination. Hence, bad effects such as algae bloom, animal defect and even diseases to human could happen once they are absorbed into the environment since water is essential chain in the hydrologic cycle [4]. Furthermore, it has been reported that river pollution in Malaysia is becoming worse every year. According to Health Impact of River Water Pollution in Malaysia by [5], about 49% of rivers in Malaysia was polluted and contaminated due to agriculture, industries and farming. Besides, most of the contributors to river pollution at Klang river basin are from agro-farm sources when 34 rivers were categorized as polluted and some of the rivers are having eutrophication phenomena because of excessive nutrients. It is proving that agriculture gives a big impact on the environment. Usually, runoff that flows from agriculture area consists of high concentration of nutrients and pesticides from agriculture practices. Therefore, Best Management Practices (BMPs) and Low Impact Development (LID) are applied to reduce the pollution and manage the runoff from agriculture area before it flows into the water bodies. These approaches may be used to overcome the problem but on the other hand, it has low ability to cater the pollutant removal consistency [6]. Agriculture pollution is one of the issues that needed to be concerned since it initiates harmful effects to humans and environment. Many agencies and researchers have created awareness towards this pollution. Moreover, the government also created environmental department to control this issue. BMPs are one of the efforts to help reduce pollution by giving practices in the agricultural system such as control the usage of pesticides in agriculture. In this practice, the farmers should N. A. Ahmad Zubairi, H. Takaijudin, K. W. Yusof A Review on the Mechanism Removal of Pesticides and Heavy Metal from Agricultural Runoff in Treatment Train A World Academy of Science, Engineering and Technology International Journal of Environmental and Ecological Engineering Vol:15, No:2, 2021 75 International Scholarly and Scientific Research & Innovation 15(2) 2021 ISNI:0000000091950263 Open Science Index, Environmental and Ecological Engineering Vol:15, No:2, 2021 publications.waset.org/10011820/pdf