Are Your Fluoride Numbers Real?

Fluoride site-management decisions are informed by analytical results. Several factors, however, can affect the quality of results and cause analytical bias. Bias on reported groundwater fluoride concentrations may result from aspects of the sampling, handling, transport, preparation, and analysis stages of the sampling program.

Fluoride is generally regarded as a conservative ion (i.e., persistently dissolved), yet several processes can partition fluoride to solid particles. This includes mineralization as fluorite or fluorapatite, and sorption onto clay or metal oxide surfaces. Entrainment of fluoride-bearing particles into groundwater samples can lead to high bias in results if digested during sample transit or during the analytical process. Conversely, certain types of particles can scavenge dissolved fluoride and lead to low bias.

Analytical techniques are also susceptible to interferences, which may produce high bias depending on the sample matrix or analytical procedure. For example, fluoride analysis by ion chromatography (Method 300.0) can overestimate concentrations in high pH samples and samples with high carbonate concentrations.

Critical evaluation of fluoride numbers may be warranted prior to investment in complex modeling efforts or making critical site-management decisions. Addressing fluoride concerns requires specialized expertise. There are opportunities for cost savings with fine-tuning of hydrogeochemical conceptual model by identifying locations where fluoride concentrations have been overestimated, thereby lowering time needed to meet remediation goals.

EHS Support is a global leader in fluoride remediation. To learn more, contact Andrew Fowler, Ph.D., senior geologist.

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