1. Chemical monitoring
PaSOC supports the use of passive sampling methods for chemical monitoring of organic compounds in water (natural or synthetic carbon-containing compounds). Many different organic compounds enter the environment as a result of human activities, and chemical monitoring is needed to protect the environment from the adverse effects that these compounds could have. Examples of such compounds are pesticides, pharmaceuticals, flame retardants, additives in personal care products, combustion products, etcetera. Traditional monitoring methods include batch water sampling, and collection of suspended matter, sediments and mussels, followed by extraction and chemical analysis.
2. Passive sampling
With passive sampling methods the target compounds are extracted in situ, by exposing a sorbent in the water for days, weeks, or months. Compounds initially accumulate in the sorbent at a rate that is proportional to their concentration in water (kinetic sampling stage). After prolonged exposure of the sampler, these compounds may reach their equilibrium concentration, which also is proportional to the concentration in the water (equilibrium sampling stage). These methods are called “passive” because compound transport to the sorbent is by ambient convection and diffusion, rather than by active sampling of a fixed water volume with a bottle or by water pumping through an in situ extraction device.
Passive sampling is often contrasted with active sampling methods. Active sampling can be continuous water sampling, grab water sampling at higher or lower frequency, or sampling of biota (e.g. fish or mussels). Whether active or passive sampling is best depends of course on the purpose of the monitoring program, the available budget, and the required accuracy. PaSOC’s position is that either approach has its pros and cons, and that the universal method that solves all of our monitoring problems does not exist. Instead: if you choose for passive sampling, do so based on the best available samplers, using the best available science. We will also be happy to support you in making a choice between passive versus active water sampling.
3. What passive sampling can provide
Passive sampling methods capture a time-integrative picture of concentration levels, thereby eliminating the risk that important emission events are entirely missed. These methods allow measurement of concentrations of freely dissolved compounds, which are proportional to chemical activity, which in turn is an important parameter in the fate assessment of organic compounds (e.g., bioaccumulation, air-water transfer). Detection limits are often well below 1 nanogram per liter, and sometimes down to the low picogram per liter range, depending on the compound and the sampler.
4. How PaSOC can help
The challenge with passive sampling methods is to calculate concentrations in the water phase from the amounts that are accumulated by the sampler, using appropriate sampler-water exchange models. These models can be empirical or mechanistic, and require calibration parameters (typically sampler-water partition coefficients and water sampling rates).
Another challenge is selecting the best alternative from the available (>20) sampler types. PaSOC supports the selection of optimal sampler types, calibration parameters, and sampler-water exchange models for a particular compound or group of compounds, based on the best available knowledge. This support is rooted in a 25-years experience with passive sampling methods, a sound knowledge of physical chemistry and chemical engineering, and an up-to-date knowledge of the scientific passive sampling literature. An overview of free and paid services can be found on the services page.
It is PaSOC’s ambition to use the best available scientific knowledge for the best achievable chemical monitoring practice, aiming to make this world a safer place.
We are looking forward to hear about your challenges in chemical monitoring, to learn from your experience, to share our knowledge, to cooperate, in order to improve the reliability of your monitoring programs.