Abstract
Urinary naphthol is an established human biomarker used for assessing both occupational and environmental exposure. However, 1-naphthol is a metabolite of the insecticide carbaryl while both the 1- and 2-isomers are metabolites of naphthalene. Thus, urinary 1-naphthol levels will reflect combined exposure to both substances, particularly at environmental levels. The interpretation of biomarkers is aided by knowledge of levels following well-characterised exposure scenarios. This study reports urinary 1-naphthol levels in five volunteers administered an oral dose of carbaryl at the acceptable daily intake (ADI, 0.008 mg/kg). The elimination half-life was 3.6 h and the mean 1-naphthol level in 24 h total urine collections, normalised for a 70 kg individual, was 37.4 µmol/mol creatinine (range 21.3–84.3). Peak levels in spot-urine samples were around 200 µmol/mol creatinine. For comparison, 327 post-shift urine samples obtained from 90 individual workers exposed occupationally to naphthalene had 1-naphthol levels from below the limit of detection (<LoD) to 1027 µmol/mol creatinine (median = 4.2, mean = 27.2). The 2-naphthol levels ranged from <LoD to 153 µmol/mol creatinine (median = 4.0, mean = 8.1). Background ranges have been reported for urine naphthols in several populations, with upper limits between 10 and 20 µmol/mol creatinine. The data reported here suggest that environmental exposure to carbaryl and naphthalene in these populations is well controlled.
Highlights
Carbaryl (1-naphthyl-methylcarbamate; CAS No 63-25-2) is a carbamate insecticide used on a variety of crops [1,2]
This study reports urinary metabolite levels found in volunteers who received a single oral dose of carbaryl at the Acceptable daily intakes (ADIs)
These data will be discussed in relation to naphthol levels measured in the urine of naphthalene-exposed workers as well as background levels in the UK population [16], resulting from environmental exposure to both carbaryl and naphthalene
Summary
Carbaryl (1-naphthyl-methylcarbamate; CAS No 63-25-2) is a carbamate insecticide used on a variety of crops [1,2]. Carbaryl is quickly metabolised to 1-naphthol which undergoes conjugation and is subsequently excreted in urine [8]. 1- and 2-naphthol isomers are major metabolites of naphthalene excreted in urine. Background population levels of 1-naphthol will generally reflect environmental and dietary exposure to a combination of both carbaryl and naphthalene. This study reports urinary metabolite levels found in volunteers who received a single oral dose of carbaryl at the ADI. These data will be discussed in relation to naphthol levels measured in the urine of naphthalene-exposed workers as well as background levels in the UK population [16], resulting from environmental exposure to both carbaryl and naphthalene
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