Analysis of Heavy Metals, Residual Pesticides, Inorganic Substances, and Leachate in Rock Wool and Coir Substrates used for Paprika Cultivation

Abstract

This study evaluated the recyclability of rock wool and coir substrates used for paprika cultivation by analyzing their compositions and potential hazards. The heavy metal contents were determined before and after cultivation, and residual pesticides and inorganic substances were measured after cultivation. The leachate generated from soaking the coir substrates was analyzed for its heavy metal, chloride ion, and salinity contents. The concentrations of copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) contained in the rock wool substrates before and after use were below the threshold values set by the Soil Environment Conservation Act for soil contamination concerns in region 1 (paddy fields, dry fields, orchards, pastures, and mineral spring sites) in South Korea. The rock wool substrate exceeded the threshold values set by the Soil Environment Conservation Act for soil contamination concerns in region 1. However, hexavalent chromium (Cr6+) was not detected, and only trivalent chromium (Cr3+), which has less of an impact on human health and the environment, was found. In contrast, the heavy metal content in the coir substrate was below the threshold set for soil contamination in region 1, confirming that it poses no environmental concerns. A residual pesticide analysis revealed that only dinotefuran was detected in rock wool. In the coir substrate, three insecticides (chlorantraniliprole, chlorfenapyr, dinotefuran) and three fungicides (boscalid, procymidone, fluxapyroxad) were detected. However, all were below the maximum residue limits set by the Ministry of Food and Drug Safety. Rock wool and coir substrates contain the inorganic components N, B, Ca, K, Mg, Mn, Na, P, and Si. The rock wool substrate was particularly high in silicon and calcium, whereas the coir substrate had a high nitrogen content. These results suggest that rock wool and coir substrates can be recycled as soil conditioners or fertilizers. Additionally, it was confirmed that the leachate generated during pre-cultivation soaking of the coir substrate could be discharged without causing environmental issues.