# Aniline – Addendum: Re-evaluation of the BAT value and evaluation of a pregnancy risk group for the BAT value: Assessment Values in Biological Material – Translation of the German version from 2025

## TL;DR

This paper re-evaluates the biological tolerance value for aniline and assigns it to a pregnancy risk group based on toxicological data.

## Contribution

The study confirms the BAT value of 500 μg aniline/l urine and assigns it to Pregnancy Risk Group B.

## Key findings

- Exposure to aniline can increase methaemoglobin levels in human blood.
- The BAT value of 500 μg aniline/l urine is confirmed as the maximum allowable level.
- A urinary concentration of 30 μg aniline/l is considered safe for pregnant women.

## Abstract

The German Senate Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) re-evaluated the data for aniline [62-53-3] to verify the biological tolerance value (BAT value) of 500 μg aniline/l urine and to assign the BAT value to a pregnancy risk group, considering all toxicological end points. Relevant studies were identified from a literature search. The critical effect of aniline exposure in humans is considered to be the formation of methaemoglobin. It must be ensured that the methaemoglobin value remains below 5%, even if the BAT value is maintained. In an experimental study, the methaemoglobin content in human blood rose from 0.72% to an average methaemoglobin value of 1.2% (maximum of 2.07% methaemoglobin) during six hours of exposure to 2 ml aniline/m3 (corresponding to the maximum concentration at the workplace, MAK value). With linear extrapolation an excretion of 224 μg aniline/l would be expected at the end of an eight-hour exposure period. Consideration of the increased respiratory volume and the critical methaemoglobin increment results in a concentration of 500 μg aniline (after hydrolysis)/l urine. The BAT value has therefore been confirmed. Due to acute toxic effects, the BAT value must be regarded as the maximum value, i. e. it must be ensured that this value is not exceeded. Sampling should take place at the end of exposure or the end of a shift.

Because the no observed adverse effect concentration (NOAEC) for methaemoglobin content in relation to developmental toxicity in humans is not known, a risk for the unborn child cannot be ruled out, even in cases of compliance with the BAT value. The BAT value is therefore assigned to Pregnancy Risk Group B. As an indication of the prerequisite for an assignment to Pregnancy Risk Group C, a concentration of 30 µg aniline/l urine has been calculated from the lowest value of the natural background range of mean methaemoglobin values in (pregnant) women. At this urinary aniline concentration, damage to the embryo or foetus is unlikely.