Assessment of Heavy Metals, Microplastic Pollution Level, and Contamination Risk in Fish Culture Ponds

Microplastics (MPs) have been found in various ecosystems and have gained global attention as an emerging pollutant. In this study, 10 water samples were collected from 10 different ponds and analyzed to assess water quality, MP abundance, characteristics, pollution levels, and contamination risks. The investigation revealed that the dissolved oxygen (DO) in 90% of the samples was slightly below the permitted limits; additionally, the biochemical oxygen demand (BOD) and chemical oxygen demand (COD) exceeded acceptable limits. Most of the samples showed higher levels of $${\text{NO}}_{3}^{ - }$$ and $${\text{PO}}_{4}^{{3 - }}$$ . The heavy metal concentrations followed the trend: Cr > Cu > Fe > Mn > Ni > Zn > Pb > Cd, with Cr exhibiting higher values in all samples. These findings point to poorer water quality. Using the water quality index (WQI) and pollution indices, in particular, the heavy metal pollution index (MPI), heavy metal evaluation index (HEI), and degree of contamination (CD), 80% of the samples were classified as highly polluted. Microscopic analysis showed that MP content ranged from 0.11 to 2.32 items/L. Most of the MP particles were fibers and fragments, colored red and blue, and were less than 1 mm in size. Scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy indicated the presence of polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). The ponds analyzed were contaminated with MPs based on the contamination factor (CF > 3) and the pollution load index (PLI > 1). The sources of MP contamination in these ponds included human activities such as household waste disposal, the disposal of large plastic debris, municipal wastewater drainage, fish feed, and fishing activities. To reduce MP contamination, the study recommends improving the monitoring system.