Quantification of quaternary ammonium compounds by liquid chromatography-mass spectrometry: Minimizing losses from the field to the laboratory.

Quaternary Ammonium Compounds (QACs) are widely used in household, medical and industrial settings. As a consequence, they are ubiquitously found in the environment. Although significant efforts have been put into the development of sensitive and reproducible analytical methods, much less effort has been dedicated to the monitoring of QACs upon sample storage and sample preparation. Here we studied the effect of storage, concentration, and extraction procedures on the concentrations of QACs in samples. Thirteen QACs selected amongst benzalkonium compounds (BACs), dialkyldimethylammonium compounds (DADMACs) and alkyltrimethylammonium compounds (ATMACs) were quantified in aqueous and solid samples using LC-MS/MS. Most QACs adsorbed on container walls could be recovered using a short washing step with MeOH containing 2 % v/v formic acid. Concentrations of QACs from aqueous solutions using solid phase extraction (SPE) with Strata-X cartridges and elution with acidified MeOH utilized to wash the emptied containers gave highly satisfactory recoveries (101-111 %). Good recoveries (89-116 %) were also obtained when extracting a spiked organic-rich synthetic soil using accelerated solvent extraction (ASE) with acidified MeOH at low solid/solvent ratio (0.4 g/20 mL). Applying the recommended methodologies to real samples collected from a Canadian wastewater treatment plant (WWTP) gave QAC concentrations in the ranges of 0.01-30 µg/L, < 1.2 µg/L, and 0.05-27 mg/kg for the influent, effluent and biosolids samples, respectively.

Fate and exposure modeling in regulatory chemical evaluation: new directions from retrospection.

The development and application of fate and exposure modeling has undergone fundamental changes over the last 20 years. This has, in part, been driven by different needs within the regulatory community to address chemicals of concern using different approaches. Here we present a retrospective look at fate and exposure model application over the last two decades keeping an international regulatory perspective and using the Government of Canada's Chemicals Management Plan to illustrate concepts. We discuss the important role fate and exposure modeling has played to help address key data gaps when evaluating the risk of chemicals for both human health and ecological reasons. Yet limitations for more widespread model application within a regulatory context remain. Consequently, we identify specific data gaps and regulatory needs with an eye towards new directions for 21st century chemical evaluation. We suggest that one factor limiting greater model application is the need for increased awareness and agreement of what chemical exposure assessment encompasses within the risk assessment paradigm. This is of particular importance today because of the increased availability of computational and high-throughput data and methods for chemical assessment allowing evaluators to potentially examine exposure from site of release to site of toxic action, thus linking exposure with toxicology. We further suggest there is a need for discussion at a global level to promote the awareness of new tools and approaches available for fate and exposure modeling and suggest that this could be organized using the aggregate exposure pathways concept.