## 3 The Effect of Biochar on the Environmental Fate of Pesticides
### Factors Affecting Biochar on Environmental Fate of Pesticides  
Due to the unique physicochemical features of biochar, it often has a high capacity for adsorbing pesticides prevalent in the soil environment. These properties are highly dependent on the feedstock (pinewood, wheat straw, rice husk, dairy manure, sugar beet tailings, and sewage sludge) and pyrolysis conditions (temperature, heating rate, and residence time), which are two critical factors affecting the amounts of functional groups on the surface of biochar [100]. For example, biochar produced at greater pyrolysis temperatures might provide more sorption sites for pesticides due to its increased surface area. However, high heating degrades the acidic functional groups on the surface of biochar, reducing its potential to adsorb \(\text{NH}_{4}{}^{+}\text{-N}\)[101,102]. In addition, it has been shown that the adsorption capacity of biochar is related to its physical and chemical properties, such as specific surface area, pore diameter size, degree of carbonization, aromaticity, etc. However, a single factor such as aromaticity is not able to explain the responding trends of sorption [103,104]. Sorption of environmental constituents, especially natural organic matter, and oxidation reactions have been established as major contributors to the aging of biochar, which might impact biochar sorption affinity for pollutants [105]. However, by lowering the amounts of functional groups on the surface, this can also result in decreased pesticide sorption. Biochar's structure and sorption capability are very variable depending on the raw materials used and the pyrolyzing conditions. The most critical element affecting the structure and sorption behavior of biochar is the pyrolyzing temperature. The yield of biochar decreases with the increase of temperature, and the pH value is mostly alkaline. The carbon content, C/N, ash content, and adsorption of pesticides basically increase with the increase of temperature, while soluble carbon content and volatile matter deficiency show the opposite trend [106]. Minerals form on the surface of the biochar after pyrolysis and clogg the pores. Ash might bind to pesticides but has a detrimental effect on sorption [107]. It may cover the reactive surfaces of biochar, masking its real pesticide sorption capability. Thus, acid washing is required to increase the specific surface area of biochar. Many factors influence pesticide sorption of biochar in soil, including biochar characteristics. Note that soil and ambient variables such as moisture, temperature, pH, and minerals impact biochar stability [108].  
The solubility, pKa, molecule size, and substituent nature of aromatic biochars all influence the adsorption mechanism. Since pH affects the surface charge of biochar and the molecular form of pesticides in soils, it is one of the most critical elements controlling the adsorption process [106]. Pesticide features such as kind, molecular size, molecular polarity, and functional groups influence sorption, desorption, and degradation in soilssupplemented with biochar [109]. The sorption mechanisms shift when the solute concentration change. Biochar can alter the fate and bioavailability of pesticides in soil, which affects the biodegradation of pesticides. This primarily depends on biochar properties, soil characteristics, and pesticide types. Clearly, further research is required to determine how long biochar in soil may continue to bind pesticides and hence influence their efficacy.