ISO 25318:2018 – Water Quality: Advanced Analysis for Emerging Contaminants

1. Advanced Analytical Techniques in ISO 25318

ISO 25318:2018 extends the water quality analysis framework established by ISO 25317, introducing advanced analytical techniques for the determination of emerging contaminants including pharmaceuticals, personal care products, endocrine-disrupting compounds (EDCs), per- and polyfluoroalkyl substances (PFAS), and microplastics in aquatic environments. The standard addresses the unique challenges posed by these analytes: ultra-trace concentration levels (ng/L to μg/L), complex matrix interference, and the need for confirmatory analysis through mass spectrometry.

A key contribution of ISO 25318 is the standardisation of solid-phase extraction (SPE) protocols for multi-residue analysis. The standard specifies sorbent selection guidelines (including hydrophilic-lipophilic balance polymers, mixed-mode ion exchange, and molecularly imprinted polymers), elution solvent systems, and concentration procedures. Recoveries for target analytes must fall within the 70–130% range, with relative standard deviations below 20% for replicate analyses. The standard also introduces isotope dilution techniques using deuterated or 13C-labelled internal standards to correct for matrix effects in LC-MS/MS and GC-MS/MS analysis.

2. Data Quality Objectives and Method Validation

ISO 25318 introduces a systematic framework for establishing data quality objectives (DQOs) specific to emerging contaminant analysis. The standard requires that the target level of quantification (TLOQ) be set at or below 30% of the relevant environmental quality standard or predicted no-effect concentration (PNEC). Method validation must include assessment of linearity (R² ≥ 0.99 over the working range), accuracy (recovery 70–130%), precision (RSD ≤ 20%), and measurement uncertainty (expanded uncertainty with k=2 coverage factor).

The standard also addresses the critical issue of laboratory background contamination for ubiquitous environmental contaminants such as phthalates, bisphenol A, and PFAS. Specific measures include the use of polypropylene rather than glass or PTFE sample containers, the installation of carbon-filtered air handling systems in laboratory areas, the use of clothing restrictions (no synthetic fleece or waterproofed garments), and the implementation of blank subtraction procedures with associated uncertainty evaluation.

3. Engineering Design Insights for Emerging Contaminant Monitoring

From an engineering design perspective, implementing a monitoring programme for emerging contaminants requires careful consideration of sampling strategy, analytical capacity, and data interpretation frameworks. Unlike conventional pollutants with well-established environmental quality standards, many emerging contaminants lack regulatory thresholds, requiring a risk-based approach to data interpretation. ISO 25318 provides guidance on the use of environmental quality standards (EQS), predicted no-effect concentrations (PNEC), and threshold of toxicological concern (TTC) concepts for data evaluation.

A practical recommendation from ISO 25318 is the use of composite sampling over grab sampling for emerging contaminant monitoring. Time-proportional composite samples collected over 24 hours account for diurnal variation in contaminant loading, which can vary by a factor of 3–10 for pharmaceuticals in domestic wastewater. The standard also recommends that sampling campaigns include at least three sampling events per season (minimum 12 events per year) to capture seasonal variations in contaminant usage patterns.