How Low Can We Go: Detection Limits and their Role in Water Quality Compliance

Safe Drinking Water Act Detection Limits and their Role in Water Quality the potential adverse effects on humans the frequency and level found in drinking water opportunity to reduce public health risk 40 CFR Part 136 Method Detection Limit MDL is minimum conc. that can be measured with 99% confidence that it is greater than zero. The RL is then 2.5 to 5 times higher. Concentrations and Equivalents %= 1 part per hundred: sea water is 3.2% salt mg/L = part per million or ppm: 1 oz of salt in 16,500 lbs of sugar ug/L= parts per billion or ppb: 1 second in 32 years ng/L= 1 part per trillion or ppt: 1 sq. inch in 250 sq. miles pg/L= 1 part per quadrillion or ppq: 1 human hair on all the heads in the world UCMR Minimum Reporting Level (MRL) is lowest conc. where recovery 50%-150% with 99% confidence and is derived from the Lowest Concentration Minimum Reporting Level (LCMRL) from multiple labs. Laboratory Methods Standard Methods for the Evaluation of Water and Wastewater, EPA Methods, AOAC Official Methods Gravimetric techniques Colorimetric techniques: UV VIS spectrophotometry Atomic Absorption Spectroscopy:AA Emission Spectroscopy: ICP Gas and Liquid Chromatography: GC , IC, and LC (HPLC) Immunoassay (ELISA) & PCR Automation has benefited: Reproducibility of sample preparation Reproduciblility sample introduction into the instrument Computerization has had the biggest impact: Instrument operation Ease of quantitation Sophistication of data reduction Quick access to libraries of standards & knowns Data collection & storage Early Method Detection Limit Study for Cr+6 Cr+6 seven replicates at spiking conc. of 0.05 ug/L (50 ppt) (between 2.5 to 5 times an estimated MDL) 0.032 0.031 0.032 0.036 0.041 0.031 0.039 Relative Standard Deviation: 11.91 Mean: 0.0346 Standard Deviation: 0.004 MDL: 0.0129 RL: 0.06 UCMR HRpir = 3.963 (S) Upper pir must be <=150% Lower pir must be >=50% Upper pir = Mean+HRpir/True Value= 102% Lower pir = Mean-HRpir/True Value= 37% California Code of Regulations Regulations Laboratory Public Perception Contaminant Candidate List: suspected to be in water no standards set under SDA <30 per 5 years MDLs MRLs Instrumentation Automation Computerization Instrument improvements: hardware, electronics, columns Detector Improvements...LC/MS/MS example EPA & Contract Labs research methods, reporting limits, and detection limits Safe Drinking Water Act Mandates a rigorous, scientifically valid process for determining risks to public Fear Misinformation Impatience Questions? Allison Mackenzie E. S. Babcock & Sons, Environmental Laboratories amackenzie@babcocklabs.com UCMR3 Seven Hormones (EPA 539) testosterone 0.1 ppt 17-a-estradiol 0.9 ppt Six PFCs (EPA 537) PFOA 20ppt PFOS 40ppt