Derivation of an occupational exposure limit for inorganic borates using a weight of evidence approach

•We derive OELs using new data and current risk assessment frameworks (e.g., IPCS).•We review reproductive and developmental toxicity and sensory irritation effects.•Sensory irritation is considered the most sensitive endpoint of concern.•We use dose–response modeling to support point of departure selection.•An OEL of 1.4mgB/m3 is recommended as an 8-h time-weighted average. Inorganic borates are encountered in many settings worldwide, spurring international efforts to develop exposure guidance (US EPA, 2004; WHO, 2009; ATSDR, 2010) and occupational exposure limits (OEL) (ACGIH, 2005; MAK, 2011). We derived an updated OEL to reflect new data and current international risk assessment frameworks. We assessed toxicity and epidemiology data on inorganic borates to identify relevant adverse effects. International risk assessment frameworks (IPCS, 2005, 2007) were used to evaluate endpoint candidates: reproductive toxicity, developmental toxicity, and sensory irritation. For each endpoint, a preliminary OEL was derived and adjusted based on consideration of toxicokinetics, toxicodynamics, and other uncertainties. Selection of the endpoint point of departures (PODs) is supported by dose–response modeling. Developmental toxicity was the most sensitive systemic effect. An OEL of 1.6mgB/m3 was estimated for this effect based on a POD of 63mgB/m3 with an uncertainty factor (UF) of 40. Sensory irritation was considered to be the most sensitive effect for the portal of entry. An OEL of 1.4mgB/m3 was estimated for this effect based on the identified POD and an UF of 1. An OEL of 1.4mgB/m3 as an 8-h time-weighted average (TWA) is recommended.