Analysis of the heavy metals and Escherichia coli contamination of liquid organic fertilizers in the local market, Sri Lanka

Abstract

Commercially available liquid organic fertilizers have gained popularity in agriculture due to their convenience and perceived environmental benefits. However, these fertilizers are susceptible to various contaminations, including heavy metals such as lead (Pb) and cadmium (Cd), as well as bacterial contaminants like Escherichia coli (E. coli). Monitoring these contaminants helps to identify potential health risks to consumers, prevent soil and water pollution, and maintain the quality of agricultural products. Therefore, this study involved a comprehensive analysis of Pb and Cd heavy metals and E. coli bacterial contaminants in two widely used liquid organic fertilizers in the local market. The samples were digested using an open-vessel acid digestion followed by the flame atomic absorption spectroscopic (FAAS) analysis. The limit of detection (LOD), limit of quantification (LOQ), matrix effect, and spike recovery were determined. The Pb concentration of one fertilizer was 3.45 (± 0.07) mg/kg with 92% recovery whereas the other was 2.87 (± 0.08) mg/kg with 91% recovery. In contrast, the Cd concentration was 0.09 (± 0.01) mg/kg and 0.11 (± 0.01) mg/kg with percentage recoveries of 93% and 90% for two fertilizers respectively. The Pb content exceeded the maximum permissible limit of 1.0 mg/kg set by the Sri Lanka Standard (SLS 1702:2121), while Cd levels remained within the limit of 0.5 mg/kg. Polymerase chain reaction (PCR) coupled with gel electrophoresis confirmed the presence of the pathogenic O157:H7 E. coli strain in both fertilizers. Thus, the results of this study confirmed the lead (Pb) and Escherichia coli contamination in liquid organic fertilizers in the local market of Sri Lanka.