On the use of high‐density polyethylene bottles for long‐term storage of total alkalinity samples

Abstract

Total alkalinity (TA) plays an important role in buffering seawater and determining how much anthropogeniccarbon dioxide the oceans can absorb and mitigate the rise in atmospheric concentrations. Total alkalinity varieswith location, depth, and time making it an important variable needed to quantify and monitor ocean acidification,and potentially for ocean alkalinity enhancement interventions. Currently, best practices are to use expensivehigh-quality borosilicate glass bottles for collecting and storing these samples. However, unlike other carbon systemvariables, TA is not affected by gas exchange meaning plastic bottles may be suitable for TA sample storage. Plasticbottles are lighter, cheaper, and less prone to breakage making them easier to handle and ship. Here, we test the suit-ability of high-density polyethylene (HDPE) for collection and long-term storage of TA samples. In two sets of exper-iments, it was determined that HDPE is not suitable for long-term storage of TA samples as there were large changesin TA over time and precision of duplicate samples was very poor. We hypothesize that HDPE plastic is slightlyporous leading to leaching of alkalinity either into or out of the bottle over time impacting the value of the sample.Use of HDPE bottles for TA samples is not recommended for long term sample storage.