From the standpoint of sequestration of carbon, reducing the emission of greenhouse gases and improving the soil fertility, biochar amendment of soil is attractive and is gaining increasing attention. While the benefits of biochar applications to soil fertility have been well articulated, the potential unintended consequences of biochar amendment to soils, especially the impact on contaminant fate, dispersal and build-up is thus far have not been fully appreciated. We carried out a series of experiments on sorption-desorption of pesticides on different types of biochars, plant uptake and persistence of pesticides from biochar-amended soils. We also investigated the efficacy of herbicides in terms of weed control in soils amended with different amounts of biochar.  We found that biochars, especially produced from wood at high temperatures (< 450^◦C), were particularly effective sorbents of pesticides. This caused decreased bioavailability of pesticides for plant uptake or microbial degradation.  We noted that the highly reactive biochars can render the applied pesticides ineffective and consequently much higher application rates may be needed for the desired pest and weed control. The implication of biochar amendment to soil and potential implications for the environmental accumulation, distribution and food safety of pesticides needs to be fully understood before recommending widespread application of biochar to soils as a climate change mitigation initiative.