On-line Monitor for Metaldehyde in Surface and Ground Water

Significance of the Topic

Monitoring metaldehyde in drinking water sources is critical due to its widespread agricultural use as a molluscicide, its persistence in the environment, and challenges in conventional treatment. Real-time tracking of trace levels below the UK regulatory threshold (0.1 µg/L) enables water utilities to react promptly to contamination events, optimise treatment processes, and ensure safe supply.

Aims and Study Overview

This study describes the deployment of an online, automated monitoring system for metaldehyde at a 36 Ml/d karstic groundwater treatment works in Hertfordshire. The objectives were to integrate a laboratory-grade GC/MS platform with flow-through sampling, validate performance under field conditions, and demonstrate reliable detection at regulatory levels across three process inlets.

Methodology and Sample Preparation

Sampling was achieved via a GERSTEL flow cell and automated solid-phase extraction (ITSP cartridges). Key steps:

• Condition ITSP cartridge with dichloromethane, methanol, and water.
• Load 7.5 mL water sample plus internal standard; dry under nitrogen.
• Elute analytes with 400 µL dichloromethane into GC vial.
• Inject 10 µL into a cooled injection system (CIS 4) for GC/MS analysis.

Applied Instrumentation

• Dual-head GERSTEL MPS 2 XT autosampler
• GERSTEL Cooled Injection System (CIS 4)
• Agilent 7000 Series GC-Triple Quadrupole MS
• GERSTEL Solvent Filling Station and flow cell
• Maestro software with PLC integration for telemetry

Main Results and Discussion

Validation under online conditions delivered:

• Linearity: r² ≥ 0.998 over the tested range.
• Within-batch precision and accuracy at 0.1 µg/L: <4% RSD and <6% bias.
• Between-batch precision and accuracy: <4% RSD and <6% bias.
• LOD of 0.003 µg/L and LOQ with <5% uncertainty.
• Instrument accuracy confirmed by proficiency tests (z-scores <0.02).

Consistent performance across varying turbidity was ensured by a three-stage filtration system maintaining <1 NTU at the inlet. Automated valve sequencing allowed sequential sampling from three process streams with reproducible flow rates (>1 L/min).

Practical Benefits and Applications

The online GC/MS approach with ITSP reduces analysis time from days to minutes, supports early warning of metaldehyde spikes, and provides high-quality data for process control. It allows water companies to optimise abstraction and treatment, lowering the risk of regulatory exceedance and protecting public health.

Future Trends and Possibilities

Ongoing work will explore the influence of dynamic water quality on system robustness, extend the platform to additional micropollutants, and integrate advanced data analytics and remote monitoring for fully autonomous operation. Scaling to multiple sites and combining with other sensor technologies could further enhance real-time water quality management.

Conclusion

The successful field implementation demonstrates that an automated, online GC/MS system with miniaturised SPE can deliver reliable, trace-level monitoring of metaldehyde in surface and groundwater. The platform offers a powerful tool for modern water utilities seeking real-time insight and regulatory compliance.

References

• Anatune Application Note AS123: Automated ITSP SPE for metaldehyde analysis
• Anatune Application Note AS134: Flow cell technique for online liquid sampling