Down down, deeper and down…

Hazel Davidson provides an overview of recent developments enabling water testing laboratories to reach lower limits of detection – but will they be low enough to meet new standards? The Water Framework Directive (WFD) revised their list of Priority Pollutants in August 2013, and updated the groundwater directive in March 2014. Many of the Environmental Quality Standards (EQS) values listed in these directives are lower than current practice, and the industry is aware of the need for lower limits of detection. However, there is some concern that it may not be possible to meet all of them in the required timescales. Priority substances include compounds considered potentially toxic to human life, and for a number of years, a list of 33 compounds was used as the basis for monitoring a range of pollutants in surface waters in order to determine the status of the water body. The list of 33 is split into Priority Hazardous Substances (PHS), Priority Substances (PS), plus a further 19 Specific Pollutants (SP), with associated EQS values listed for each compound, and the monitoring of data should ensure all member states are working to comply with the WFD aim of achieving ‘good status’ for all surface water. [caption id="attachment_39937" align="alignright" width="350"]
Table 1. Examples of the new Priority Hazardous and Priority Substances[/caption] There were 12 new additions to the Priority Hazardous and Priority Substances lists, plus the top two compounds in Table 1 were reclassified as Priority Hazardous rather than Priority Substances. This brings the total of Priority Pollutants to 48. A further change was the additional requirement of analysing biota (fish or shellfish), rather than just the water itself (labelled in red in Table 1, uPBT ubiquitous Persistent Bioaccumulative and Toxic). The pollutants will be concentrated in the tissues of the organisms over a period of time, and thus allow a better indication of cumulative toxins. A good example of the requirement of very low detection limits is Cypermethrin, where the listed EQS is 8x10^-6. This equates to 0.000008 ug/l, or 0.008 ppt, and is not currently achievable. The timescales for implementation are:

• Transposition of revised directive within 2 years – August 2015.
• Existing PHS, PS and SP compounds: revised EQS apply from 2015 (assuming analytical methods available by December 2014), with compliance by December 2021.
• New PHS and PS compounds: apply from December 2018, with compliance by 2024.

The requirement for lower detection limits can be achieved by improved instrumentation – for example, the updated Skalar spectrophotometric systems for cyanide, phenol and total organic carbon can be up to a factor of 20x better than existing instrumentation. [caption id="attachment_39941" align="alignright" width="350"] Table 2: Comparison of Detection Limits[/caption] A range of standards at known concentrations is prepared, and analysed by the instrument. The software on the instrument sets up the calibration graph, and when unknown samples are analysed, the response is read from this graph, allowing the concentration of the analyte in the sample to be calculated. This improved performance allows much lower reporting limits (Table 2). The huge range of organic compounds can present problems, both in sampling and analysis, and there are some critical factors which need to be considered. Organics can exist in the following three physical phases: -       Truly dissolved – highly variable solubilities (see Table 3). -       Colloidal suspension – very small droplets suspended in the water – can appear cloudy. -       Free product – either as an LNAPL (floating) or DNAPL (below a water column). [caption id="attachment_39944" align="alignright" width="350"] Table 3: Examples of density and solubility in a range of VOCs[/caption] Most organics are not very soluble in water, and therefore methods are required to extract the compounds, either by the use of organic solvents for semi or non-volatile organics, or by measuring the concentration in the headspace above a water sample for volatile organic compounds. The correct sampling and storage of waters for organics, particularly VOCs, is critical. It is also of great importance that sampling staff are aware of the end use of the data. For example, in groundwater from a borehole, it may only be the truly dissolved species which are of concern, in which case the samples should be filtered prior to analysis. If an effluent is being monitored, then the total loading, including any sediment, may be required, in which case the samples should not be filtered. Filtering with cellulose filters, or standard laboratory filter papers, will remove most free product and colloidal organics, leaving only the truly dissolved. Analysis of VOCs in waters is usually performed using GCMS with a headspace introduction system, although very clean waters can be analysed by purge and trap systems. Neither technology is particularly new. It is not possible to pre-concentrate the samples, due to loss of VOCs, and neither is it really feasible to increase the volume of sample taken (as it is the headspace, not the liquid itself which is injected onto the GC column), so improving the LoD will need to be by instrumental improvements. For analysis of extractable organics such as pesticides, these can be improved by using larger volumes of sample and concentrating the organic compounds using an SPE column, and/or using a large volume injector on the GC/GCMS system. More recent innovation includes the use of SPME, which is an automated version of SPE, avoiding the use of large volumes of solvent – the organics are extracted from the water onto an integrated column, which allows a greater concentration of the compounds of interest, thus improving the detection limits. In summary, for samples to produce meaningful results, in every stage from sampling, storage, filtration (or not), extraction (or not), and instrumental analysis, it is vital for correct protocols to be followed, and the lower the detection limit required, the more important all these factors will be. A discussion on the difficulties likely to be experienced with the new WFD EQS values will also be covered during the conference. Author Hazel Davidson is chair of the EIC Laboratories Working Group and Technical Marketing Manager for DETS Ltd the analytical services company. Hazel will deliver a presentation at the WWEM 2014 Conference (www.wwem.uk.com) on Thursday 6^th November.