Experimental factors influencing the bioaccessibility and the oxidative potential of transition metals from welding fumes

Inhalation of welding fumes (WF) containing high levels of transition metals (Cr, Cu, Fe, Mn, Ni ) is associated with numerous health effects. Transition metals are known to catalyze the production of ROS and their reactivity depends on the nature of the medium in which they are solubilized. However, the measurements of the oxidative potential (OP) and transition metals bioaccessibility depend on several physico-chemical parameters and may be subject to several artifacts (particle loss, aging and physico-chemical evolution in air, etc.), that alter their representativeness during sampling, transport, storage, processing and/or analysis. The aim of this work is to investigate the influence of the experimental conditions that may affect the bioaccessibility of transition metals and their OPs on stainless and mild steel WF extracts produced in the laboratory using a controlled generation bench. In this work, we mainly investigated the effect of the soluble fraction of the metals. Two different extraction fluids mimicking physiological conditions were chosen for the solubility study: a phosphate buffer solution and the Hatch s solution. Three different extraction times were tested to determine the optimum time required to register a significant OPDTT using the dithiothreitol (DTT) method. The commonly used storage conditions of WF after sampling were investigated by varying parameters such as duration, temperature and atmospheric conditions. The results showed that experimental conditions can significantly affect the OPDTT and metal bioaccessibility analyses. Hatch s solution gives higher solubility values for Cr, Cu and Ni than those measured in the phosphate buffer. Mn is highly sensitive to DTT and shows close solubility values in the two liquids. Therefore, the phosphate buffer was selected to perform bioaccessibility and OPDTT measurements as it is easier to prepare and analyze. Regarding the extraction time, the OPDTT is related to the amount of solubilized metals and to their nature. The extraction time of 0.5h allows a higher measurement frequency and offers a better sensitivity to the OPDTT by probably limiting complexations, interactions between metals and precipitation. Limiting the OPDTT measurement to the soluble phase may lead to an underestimation of the true OPDTT value, although the soluble OPDTT remains the major contributor to the total OPDTT. In addition, storage conditions affect the solubility of metals and the OPDTT of WF samples. The results show that Mn is the element most affected by these changes. Storage time and temperature seem to have an effect on the physical or chemical evolution of the WF, which can modify the measurements of OPDTT and the solubility of Mn. However, storage under inert gas N2(g) limits the changes in terms of OPDTT and solubility. To overcome the biases associated with the aging of WF samples during storage prior to analysis, on-line measurements of OPDTT could provide an alternative to filter sampling of WF, favoring its use as a real-time marker of occupational exposure to WF.