2,3,3',5,6-Pentachlorobiphenyl is primarily used in research and environmental studies as a reference compound for analyzing polychlorinated biphenyls (PCBs). It helps in understanding the behavior, distribution, and impact of PCBs in ecosystems. Due to its persistence and toxicity, it is also studied for its effects on human health and wildlife, particularly in assessing bioaccumulation and long-term environmental contamination. Additionally, it serves as a standard in analytical chemistry for calibrating instruments and validating methods to detect and quantify PCB levels in various samples, such as soil, water, and biological tissues.