Appendix 2. Rapid screening methods for Harmful Algal Blooms toxins.

Abstract

At the core of all national harmful algal bloom (HAB) programs are the monitoring programs needed to detect HAB toxins in shellfish, fish, water, or other resources sufficiently early to take management actions (Anderson et al. 2001). These programs measure toxins produced by multiple species of algae, with the methods used varying dramatically in scope and complexity due to the types of toxins that need to be detected, the nature of the affected resource, and regulatory requirements. Some of the methods developed for analysis of shellfish tissues and algal blooms can be of direct use in desalination plants for analysis of toxins in water – both the raw, untreated water before desalination, and the treated, fresh water. A major concern, however, are the detection limits of the assays. All analytical methods have limits of detection (LODs) and the choice of a method should be consistent with potential bloom concentrations and possible toxin levels. With desalination plants, toxins need to be measured at exceedingly low levels in water, whereas shellfish concentrate toxins to much higher levels. A recent study summarized the epidemiological data for four common algal toxins (Laycock et al. 2010) and estimated the potential contamination of water that might enter a desalination plant during major blooms. The assessment was based on a hypothetical (and dense) bloom of toxic algae consisting of 10 7 cells/L with a toxin cell quota of 40 pg toxin/cell. If all of that toxin were released from the cells into the water, that would give a concentration in seawater of 400 μg/L. An alternative approach to estimating the total amount of toxin present in a bloom is given in Chapter 1 (Table 1.4), where the amounts of toxin contained in hypothetical blooms of various common HAB species are presented. The values range from a few hundred to 1,000 μg/L. Given that 99% or more of a toxin is likely to be removed by thermal or reverse osmosis desalination (Chapter 10), the sensitivity of an analytical method must therefore be at least 0.1 – 1.0 μg/L or 0.1 – 1.0 ng/mL. Therefore, analysis of water samples for dissolved or particulate toxins (i.e., inside algal cells) will require high sensitivity methods, such as enzyme-linked immunosorbent assays (ELISAs). For example, the LOD for saxitoxin (STX) using the Abraxis STX ELISA kit is 0.02 ng/mL and there is similar sensitivity for domoic acid. This appendix presents details on simple screening methods for HAB toxins. More complex analytical methods are described or cited in Chapter 2. The screening methods are presented here as a guide to desalination plant staff who wish to conduct on-site analyses. These analyses could be of raw intake water, treated water, or algal cell extracts from monitoring programs (Chapter 3). The example assays are restricted to four HAB toxins i.e., saxitoxins, domoic acid, microcystins/nodularins, and anatoxin-a. Although sample preparation procedures may differ for the other HAB toxins not include here, the commercial ELISA kit protocols are similar to each other. Sample preparation procedures, however, vary depending on solubility of the toxins, source (e.g., phytoplankton, shellfish, or cyanobacteria) and method of analysis. Sample preparation methods will be described in detail, as will procedures used to obtain samples. Methods of analysis other than ELISA are also presented. Lateral flow tests (such as the Scotia tests) are described as simpler alternatives to the ELISA kits. The advantages and disadvantages of both tests will be discussed.