Pesticides and heavy metals in sediment core samples from a coastal area in Japan

Concentrations of the pesticides diuron, Irgarol 1051 and fenitrothion and the heavy metals cadmium, copper, manganese, nickel, lead, and zinc were determined in sediment core samples (n = 45) from the Seto Inland Sea in Japan. The pesticides were analyzed using a Shimadzu high-performance liquid chromatography system equipped with a UV-Vis detector. The heavy metals were analyzed using inductively coupled plasma atomic emission spectroscopy. The highest diuron, Irgarol 1051, and fenitrothion concentrations were 415, 328 and 119 ng g–1 by dry weight, respectively. The highest cadmium, copper, manganese, nickel, lead, and zinc concentrations were 2.77, 3490, 3011, 157, 188 and 859 mg kg–1 by dry weight, respectively. These concentrations were found in sediment cores collected near the mouth of the River Yodo in Osaka Bay. The ages of the sediment core samples were estimated using radioisotopic dating techniques, and the maximum pesticide and metal concentrations were associated with periods in which anthropogenic activities occurred on land. For example, the maximum diuron and Irgarol 1051 concentrations coincided with the time these pesticides were mostly used as antifoulants as replacements for organotin compounds (in the 1990s and 2000s). Generally, the highest heavy metal concentrations were in samples dated to the 1960s and 1970s, a period of high economic activity. Sediment samples from near the coast contained high concentrations of both heavy metals and pesticides further confirming that anthropogenic activity has affected heavy metal and pesticide concentrations in the studied coastal area. The concentrations were particularly high in areas close to cities with high population densities (such as Osaka Bay) and in areas in which rivers that pass through areas with high population densities enter the Seto Inland Sea (such as Kure Bay and Harima-nada). The contaminant concentrations were lower in the surface samples than in the deeper layers of the sediment cores. Sediment is a potential source of both pesticides and heavy metals through processes such as recirculation, so pesticides and heavy metals in sediment pose risks to aquatic organisms.