Objective To assess the relationship between workplace concentration and biological monitoring level of dimethylacetamide (DMAC), and to establish its occupational biological exposure limits.
Methods Urine samples of 32 workers exposed to DMAC from a 4, 4'-diaminodiphenyl ether plant before and after work shifts on day 1, 2, and 5 were collected to detect urinary N-methylacetamide (NMAC) by gas chromatography. Air samples were collected with individual samplers during work shifts to detect DMAC concentration. Multiple regression analysis was used to assess the correlation between urinary NMAC and air DMAC, working years, and age. Meanwhile, occupational health surveillance data were collected to analyze dose-effect relationship.
Results The 8h time weighted average concentration of DMAC in workplace air was (121.32±164.31)mg/m3 (1.30-818.20mg/m3), and 26 air samples exceeded the national occupational limits of DMAC (20 mg/m3) with an unqualified rate of 81.25%. The preshift and post-shift urinary NMAC concentrations were not different among different workdays (Ps > 0.05). There was a positive relationship between post-shift urinary NMAC concentration and air DMAC concentration in workplace, with a regression equation of lgρNMAC (mg/g)=0.303+0.677lgωDMAC (mg/m3) (R2=0.725, F=63.18, P < 0.001).
Conclusion There is no obvious accumulation of NAMC in urine of workers exposed to DMAC. Post-shift urinary NMAC concentrations are significantly correlated with DMAC concentrations in air, displaying a log-transformed linear relationship. Any urinary NMAC after work shift during work week could be used for DMAC occupational exposure assessment. According to the national standard for DMAC in workplace air and the derived regression equation, the occupational biological limit of urinary NMAC is recommended as 15.27 mg/g for workers exposed to DMAC after shift.
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