After All these Years – Holding Times Still Unclear!!!
The US EPA published its Proposed Rules on October 22, 2019 (https://www.govinfo.gov/content/pkg/FR-2019-10-22/pdf/2019-22437.pdf); Docket ID No.: EPA‑HQ‑OW‑2018-0826 titled 40 CFR Part 136, Clean Water Act Methods Update Rule for the Analysis of Effluent. Table II contains the required containers, preservation techniques and holding times.
Two holding-time definitions are the subject of this discussion: cyanide holding times and preservation for tissues, solids, and mixed-phase samples.
Cyanide, total and available (or CATC) and free holding times are defined as 14 days. The cyanide method follows a two-step process, distillation followed by analysis. It is unclear if the holding time is for distillation or for both distillation and analysis. The analytical method states that the samples can be placed in cold storage if analysis is not performed following distillation. It is unclear about the specificity of the analysis time following distillation.
Holding times for solids, mixed-phase and tissue samples are also listed on the table. The holding time for tissue samples cannot be practically achieved. The stated holding time for tissue samples is 24 hours preserved at ≤ 6°C. The holding time stated for tissue samples collected in the field is impractical unless the laboratory is local, or the sample is frozen in the field with dry ice. Freezing in the field with dry ice is not specified as an option on Table II or in the footnotes referenced. The result is that, in most cases, the sample is to be transported to the laboratory in 24 hours. This is especially impractical when sampling remote areas or in the middle of the water body.
Most laboratories do not perform analysis of tissue samples, so these samples typically must be transported to a shipping location offering overnight delivery by a common carrier. Most tissue samples are analyzed for organics or metals. Typically, for aqueous samples, as with semivolatile samples, the holding time is 7 days prior to extraction preserved at ≤ 6°C. For tissue samples, A holding time of 48 to 72 hours preserved at ≤ 6°C (to accommodate collection and transport to the laboratory) should be considered prior to freezing samples at the laboratory.
A request for clarification has been submitted to the US EPA by Environmental Standards for both cyanide and tissue sample holding times. Stay tuned …