Multiplexed Workplace Measurements in Biogas Plants Reveal Compositional Changes in Aerosol Properties.

Anaerobic digestion is an emerging technology producing energy from renewable resources or food waste. Exposure screenings, comprising hazardous substances and biological agents, at different workplaces are necessary for a comprehensive overview of potential hazards in order to assess the risk of employees in biogas plants. In order to analyse these parameters, workplace measurements were conducted in seven full-scale anaerobic digesters. Personal and stationary sampling was performed for inhalable and respirable particles, volatile organic compounds, ammonia, hydrogen sulphide, carbon monoxide, and carbon dioxide. Furthermore, concentrations of the total cell count, endotoxins, and fungi-down to species level-were determined in comparison to windward air. Sequencing of the 16S rRNA genes was utilized for the determination of the bacterial composition inside the biogas plants. Measurements of hazardous substances show hardly values reaching the specific occupational exposure limit value, except ammonia. An approximate 5-fold increase in the median of the total cell count, 15-fold in endotoxins, and 4-fold in fungi was monitored in the biogas plants compared with windward air. Specifying the comparison to selected workplaces showed the highest concentrations of these parameters for workplaces related to delivery and cleaning. Strikingly, the fungal composition drastically changed between windward air and burdened workplaces with an increase of Aspergillus species up to 250-fold and Penicillium species up to 400-fold. Sequence analyses of 16S rRNA genes revealed that many workplaces are dominated by the order of Bacillales or Lactobacillales, but many sequences were not assignable to known bacteria. Although significant changes inside the biogas plant compared with windward air were identified, that increase does not suggest stricter occupational safety measures at least when applying German policies. However, exposure to biological agents revealed wide ranges and specific workplace measurements should be conducted for risk assessment.

Inhalation and dermal exposure of workers during timber impregnation with creosote and subsequent processing of impregnated wood.

OBJECTIVES: Coal tar creosote oils are used as highly effective wood protectants for, e.g., railway sleepers, utility poles and marine pilings. For impregnation of wood, the hot creosote oil is mostly applied in vacuum processes and by hot-and-cold dipping. From the perspective of an occupational hygienist, creosote tar oils are problematic because they have a number of hazardous properties, including carcinogenicity. We have studied inhalation and dermal exposure in six and four impregnation plants, respectively, in Germany. Some plants were visited repeatedly, for up to five measurement campaigns conducted over several years. Inhalation and dermal exposure resulting from vacuum impregnation and from hot-and-cold dipping, as well as secondary exposure resulting from assembly of impregnated railway sleepers have been measured. Accompanying, human biomonitoring of the employees has been performed. METHODS: Inhalation exposure was measured using personal air samplers, collecting particles and vapours simultaneously. Dermal exposure was investigated by whole body dosimetry using disposable chemical protective coveralls and split leather gloves. 18 polycyclic aromatic hydrocarbons (PAHs) have been determined separately by high performance liquid chromatography (HPLC) or gas chromatography-mass spectrometry (GC-MS), respectively. For human biomonitoring 1-hydroxypyrene (1-OHP) in urine related to creatinine has been measured using HPLC. Both, pre- and post-shift values have been determined for this metabolite. RESULTS: Dermal exposure towards pyrene and the sum of the determined 18 PAHs as well as inhalation exposure to naphthalene, pyrene and the sum of the determined 18 PAHs are presented in this paper. The plants performing vacuum impregnation have employed different constructive, technical and organisational measures, and some measures have also changed between the different measurement campaigns. We have found that cooling the vacuum impregnation vessel before unloading can reduce inhalation exposure to about one-third. However, our data shows that installation of structural or technical risk management measures (RMM) did not always reduce the exposure as intended, and can even lead to increased exposure in adverse constellations. Dermal exposure was strongly affected by differences in the working procedures. Measurements performed during assembly of impregnated railway sleepers indicate that secondary exposure leads to lower inhalation, but similar dermal exposure compared to the impregnation processes. Also 1-OHP excretion rates are similar after impregnation process and after assembly of impregnated railway sleepers. CONCLUSION: Our recent data underlines that efficient reduction of the exposure resulting from impregnation with creosote requires sophisticated risk reduction strategies. Structural measures such as the enclosure of the loading area and technical measures like local exhaust ventilation shall be coordinated carefully with organisational measures and provision of personal protective equipment. The data presented here represents a broad bandwidth of current workplace situations in the creosote oil processing industry and is therefore suitable for risk assessment in related plants as well as under regulatory frameworks like the European Biocides Regulation. Each plant in this investigation was unique. Together they represent the whole width of this branch in Germany. Additionally, the number of plants and exposed workers is limited and relative low. Therefore, a comprehensive consideration and statistical analysis were not feasible.