Effect of cadmium concentration on microbial abundance in rice field soils: A case study of Tallo watershed, Makassar

Abstract

Soil contamination with cadmium (Cd) is a critical issue that demands urgent action, mainly due to its lasting impacts on both ecosystems and human health. In particular, Cd levels in the Tallo River exceed the maximum threshold set by environmental quality standards, which poses a contamination risk to rice farms in the Tallo watershed. Cd contamination in rice Nields not only affects human health and reduces crop productivity but also has the potential to disrupt balance of soil microbial communities, which play a vital role in maintaining soil health. This study aims to analyze the effect of Cd contamination on soil microbial abundance in rice Nields around the Tallo watershed, Makassar. The measurement results showed that Cd levels in three locations ranged from 0.151 to 0.161 ppb, which is still below the pollution threshold. However, despite these relatively low Cd levels, microbial populations varied significantly across the sites, suggesting an impact even at sub-threshold concentrations. Bacterial abundance at site L1 measured 7.4 × 107 CFU/g dry soil, while L2 and L3 exhibited higher counts of 5.6 × 109 and 4.1 × 1010 CFU/g dry soil, respectively. Fungal abundance followed a similar trend, with L1 showing 7.4 × 104 CFU/g dry soil, L2 at 5.1 × 105 CFU/g dry soil, and L3 reaching 4.8 × 107 CFU/g dry soil. Interestingly, L3, located farther from the Tallo River in the Pampang area, exhibited the highest microbial abundance and the lowest Cd levels (0.151 ppb). In contrast, site L1, positioned closer to the Tallo River and the Makassar industrial zone, showed the highest Cd concentrations and the lowest microbial abundance. These findings suggest that Cd contamination can negatively affect soil microbial abundance even at sub-threshold levels. This impact is likely attributed to the sensitivity of soil microbes to heavy metals, which can impair their growth and metabolic functions.