The presence of heavy metals in freshwater is a severe problem humanity faces. Remedies with high removal efficiency of heavy metals from contaminated water are crucial. However, existing studies often neglect effluent quality per World Health Organization (WHO) standards. Also, the reported conditions are either unrealistic to the actual contamination levels or unsuitable for large-scale applications. Here, we report the fabrication of zwitterionic graphene oxide (GO) by incorporating a pH-responsive group (i.e., Lysine) using N, N′-diisopropylcarbodiimide (DIC) as a coupling agent. The modified GO-Lys was then coated on a commercially available 0.45-μm Nylon membrane and was tested for selective removal of toxic heavy metals from synthetic water and human blood plasma samples while allowing essential metal ions. Consequently, lead was the most retained toxic metal (i.e., 99.99% retention with effluent quality meeting WHO standards) among nickel, arsenic, cadmium, and mercury (i.e., between 50 to 80% retention). These composite membranes also displayed excellent fouling resistance and inhibited bacterial adhesion onto the membrane surface, while maintaining stable performance over a long time and critical transmembrane pressure conditions. This research marks a significant advancement in environmental technologies, providing an effective solution for selectively removing heavy metal pollutants, with a particular focus on lead detoxification applications.