By: Dan Kroll
There is little doubt that our water supplies are vulnerable to intentional contamination. The heightened sense of the need for security in the water industry since 9/11 has resulted in the need to respond to and investigate potential contamination incidents on a regular basis.
Responding to an event
The EPA recommends breaking the response to a potential incident into 2 tiers of testing; core field testing and advanced field-testing. The EPA recommendations for core field-testing includes radioactivity, cyanide, chlorine residual, pH and conductivity. These are common parameters and quick, easy to use field methods are available for on-site testing for all of the listed parameters.
Depending on the situation a responder may or may not wish to perform more advanced field-testing on a given site. The EPA recommends a variety of possible tests that may be included in expanded field-testing.
There are a wide variety of tools, kits and instruments that could be readily adaptable to expanded field-testing. Many of these methods are new and unproven and, caution should be the rule when initially using them until confidence has been built-up as to their ability to provide accurate results.
Toxicity tests
Toxicity is the ability of a chemical or mixture of chemicals to cause a living organism or biological system to undergo adverse effects upon exposure. These effects can include negative impacts on survival, growth, reproduction, etc. Toxicity tests are laboratory experiments, which attempt to detect or quantify toxicity in a sample by measuring the results that exposure produces on standard test organisms.
Chemiluminescence: One method of monitoring toxicity is based upon chemiluminescence. This method is the one used in the Severn Trent Services EcloxTM kit. The reaction of luminal and an oxidant in the presence of horseradish peroxidase, which results in the chemical production of light or chemiluminescence, can be used to detect the presence of toxins.
Bioluminescence: Another way to monitor toxicity is based on the production of light by various species of luminous bacteria. CheckLight LTD from Israel has developed a system based on inhibition of light production from the bacteria Photobacterium leiognathi. This system has the ability to use different buffer screening systems to differentiate between organic pollutants and metal toxins.
Bacterial respiration: Another method for measuring toxicity is the inhibition of bacterial respiration. PolyToxTM sold by InterLab Supply uses standard dissolved oxygen electrodes to measure respiration of a specially formulated bacterial culture that is sold under the PolyToxTM brand. Oxygen consumption is a good measurement of overall bacterial health, however this method does present some problems.
Testing with Daphnia and other Invertebrates: The utilization of invertebrates such as the water flea Daphnia has long been a mainstay of the toxicology laboratory. Strategic Diagnostics offers a variety of test kits in their MicorBioTest line. These tests make use of a variety of different organisms including; Tetrahymena thermophila, Brachionus calyciflorus, Brachionus plicatilis, Thamnocephalus platyurus and several Daphnia species. Toxicity in many of these tests is judged by the ingestion or failure to ingest red microspheres that are clearly visible in the organism’s digestive tract. This is a much easier endpoint to judge than traditional assays that look for lethality or changes in behavior.
All toxicity-testing methods require knowledge of a base line. Also, some toxicity methods may be too sensitive when testing in the distribution system. Water treatment chemicals or simply common constituents of drinking water such as trace metals that are not toxic to humans may adversely affect them. The choice of whether or not to use toxicity methods depends a lot on the resources available for such testing. A dedicated program that maintains some knowledge of baseline conditions can take a sizeable amount of resources. Also, due to the differences in response to various toxins from different toxicity methods, it is often a good idea to utilize more than one method or back them up with subsidiary tests such as the ones provided in the EcloxTM kit. If proper techniques, an understanding of their limitations and knowledge of normal conditions are utilized, rapid toxicity testing can be a valuable tool in the forensic investigation of water security breeches.
Read this article in its entirety here.
This article was originally published on WaterWorld.com.
