The Measurement Principle

The ToxProtect monitors the swimming activity of fish in an aquarium fed with drinking or mains water. The location of up to 10 fish and their activity is monitored continuously. Fish react sensitively to the presence of toxins and change their behaviour. The use of fish to detect toxins is an established method.

The test organisms react sensitively to most substances harmful to humans. Toxicity data are available for almost every combination of fish and toxin. To use the ToxProtect to monitor chlorinated drinking water, a dechlorination substance can be added.

The movements of the fish lead to interruptions in light barriers located in the instrument which register the entire volume of the aquarium. The activity of the fish (interrupts per minute per fish) is calculated from these interruptions. If these values fall below a pre-defined threshold, an alarm verification system is activated. In addition, immobile fish at the bottom and top of the aquarium are also registered.

The fish species can be determined by the user, the fish should be however active and have a length of 4-6 cm.

Toxicity Detection

The ToxProtect detects changes in the swimming activity of the fish due to intoxication and evaluates the measurement data for alarm events. The thresholds for the alarm triggers can be set individually. High priority of the alarm emission is given to fish at the top and bottom of the aquarium, which could indicate mortality.

The ToxProtect detects for example the respiratory toxin potassium cyanide within 10 minutes at a concentration of 1 ppm.

Alarm Verification

Due to naturally occurring random variations in fish behaviour, each alarm criterion is fulfilled from time to time by accident. Hence, in order to prevent false alarms, a verification system is required. This is achieved by decreasing the illumination (turning the light off) inside the aquarium during the verification period.

Normally, this leads to a dramatic increase in fish activity. Under toxic conditions, however, this may be different. Hence, by monitoring the "increase" in activity or lack of it during modified illumination, it is possible to accept or reject the initial alarm automatically.

Operation Monitoring (Hardware Alarm)

The ToxProtect is equipped with internal sensors which refer to possible error functions. The following parameters are monitored:

• sample flow
• drain blockage
• temperature decrease
• accidental or unauthorised ambient light in the aquarium
• high chlorine concentration