Sources and factors influencing microplastic concentration during monsoon season in the Ganga River, Bihar, India

Abstract The aquatic ecology is becoming more vulnerable to the harmful effects of microplastics (MPs) pollution. One of India’s longest rivers, the Ganga, is home to an enormous variety of wildlife. The Ganga River receives untreated residential and industrial waste from major Indian cities situated on its banks, in addition to traffic trash that is mostly responsible for the occurrence of MPs. The purpose of this study is to clarify the distribution of MPs in the Ganga at different sampling sites in the Patna area during the monsoon season based on their size, shape, color, concentration and polymer types. MPs occurred at all sites and were dominated by fibres and fragments. Mean concentration across sites was 858.5 ± 224.3 items/1000 L, with the highest level in upstream rural region Doriganj near Chhapra (1025.5 ± 94.73 items/1000 L). Further, MPs abundance were correlated strongly with population density (R = 0.92, p < 0.05), urbanization (R = 0.90, p < 0.05) and number of drains (R = 0.70, p < 0.05), and moderately with rainfall (R = 0.40, p < 0.05) within 2 km buffers, while showing a negative association with runoff. Principal component analysis confirmed anthropogenic pressures as the primary driver, with rainfall as a secondary seasonal influence. These results indicate that dense settlements and drainage connectivity, amplified by monsoon precipitation, control MP inputs. The findings provide baseline evidence for Bihar’s urban reaches and support targeted actions on solid-waste management, drainage outfall upgrades, and pre monsoon monitoring to identify hotspots and track progress. Graphical Abstract