Abstract:

The metabolism of mequindox and the food safety evaluation of its metabolite 3-methyl-quinoxaline-2-carboxylic
acid (MQCA) in the sea cucumber Apostichopus japonicus were investigated. The juvenile sea cucumbers were divided
randomly and exposed to seawater containing 2, 4 and 6 mg/L mequindox for 24 hours. Subsequently, Apostichopus
japonicus were placed into clean seawater for 96 hours for the depletion experiments. The samples were collected during
the exposure and depletion and were detected for the contents of mequindox and MQCA by high performance liquid
chromatography. The data were processed with software DAS 2.0 and SPSS 13.0. The mequindox in seawater was rapidly
absorbed by Apostichopus japonicus, and the peak concentrations (Cmax) were 0.89, 1.73, and 2.56 mg/kg, respectively at 2.5,
1.5 and 1.5 h during the exposure period. The bioconcentration factors (BCF) were 0.45, 0.43 and 0.43, and the area under
the curve (AUC) values revealed a positive correlation with the exposed concentrations (R2 = 1). The depletion of mequindox
in Apostichopus japonicus was also rapid, and 85% of mequindox was excreted or metabolized in 0.5 h. Mequindox became
undetectable after 72 h elimination. MQCA was identified as one of the metabolites of mequindox. It was detected at 15 min
exposure, and increased to the peak concentration of 29.2 μg/kg at 24 h during the exposure period (6 mg/L group).
Depletion of MQCA was slow, and remained in Apostichopus japonicus for long-term. The food safety of grown-up
Apostichopus japonicus was evaluated based on the safety index (IFS), and the IFS of MQCA in grown-up Apostichopus
japonicus was 1.23 × 10－4 (far less than 1) with no effect on the food safety.

Key words: juvenile Apostichopus japonicus, mequindox, metabolism, 3-methyl quinoxaline-2-carboxylic acid (MQCA), food safety evaluation