Pollution risk assessment in Samsun - Giresun coastal rivers; a combined approach with statistical analysis and water quality index

Water quality, sediment quality and microplastic diversity at the discharge points of Yeşilırmak River, Terme Stream, Cevizdere Stream, Melet Stream, Aksu Stream and Harşit River in Samsun-Ordu-Giresun provinces were investigated. Field studies were carried out seasonally between November 2020 and August 2021. Microplastics were determined by some physico-chemical parameters and heavy metal analyzes in water and sediment samples. Analysis results were classified according to the Water Pollution Control Regulation (SKYY) and Surface Water Quality Regulation (YSKY). Determined microplastics were classified according to type, color and polymer types. Statistical analyzes such as ANOVA, correlation and cluster were applied to the results obtained from the water and sediments samples. The mean values of water temperature, dissolved oxygen (DO), electrical conductivity (EC) and total dissolved matter (TDS) at all stations were class I water quality. The average pH in all stations is in the range of 8.66-9.30 and it is basic. Total phosphorus was found to be class III in Yeşilırmak River and class II in the rest of the rivers according to the water quality control regulation (YSKY). Harşit River was in class II water quality, while the rests were classified as class I in terms of biochemical oxygen demand (BOİ5). Turbidity was recorded as 21.02, 8.20, 11.25, 14, 67.68 and 19.50 NTUs in Yeşilırmak River, Terme Stream, Cevizdere Stream, Melet Stream, Aksu Stream and Harşit River, respectively. Aluminum (Al) concentrations in water were measured above the permissible environmental quality standard at all stations. Chromium (Cr), nickel (Ni), arsenic (As), manganese (Mn) and lead (Pb) are in class I category at all stations and seasons. Iron (Fe) was determined as class II in the Aksu Stream and Harşit River and was as class I in the rest of the rivers. Water quality index (WQI), heavy metal pollution index (HPI) and heavy metal evaluation index (HEI) were calculated in water samples. Contamination factor (CF), geoaccumulation index (Igeo), ecological risk factor (Eri), enrichment factor (EF) and pollution load index (PLI) were calculated for sediment samples. The amount of microplastic in water samples (pieces/m3) was 55 in Yeşilırmak River, 51.25 in Terme Stream, 44.75 in Cevizdere Creek, 58.5 in Melet River, 43.75 in Aksu Creek and Harşit River. In sediment samples, the amount of microplastic (pieces/kg) was found to be 300.75 in Yeşilırmak River, 133 in Terme Stream, 144.5 in Cevizdere Stream, 242.75 in Melet River, 106 in Aksu Stream and 195.75 in Harşit Stream. According to the results of infrared spectrometry (FT-IR), the ratio of polymer types detected in all stations was 41.67% PP (Polypropylene), 31.25% PES (Polyester) and 27.08% PA (Polyamide) polymer.