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Rat toxicology reports – Expert Reaction

1.1.1 A report has emerged from an unnamed lab that claims to have detected 1080 in the dead rats collected on the West Coast.

This second report contradicts the lab results released by the Department of Conservation (DoC) last week. DoC commissioned Manaaki Whenua - Landcare Research to test eight dead rats and one weka, and found no residue of 1080 toxin. Post-mortem tests by Massey University vet school could not determine the cause of death.

Landcare Research tested the dead rats for the chemical fluoroacetate, while the conflicting lab report claims to have tested for both fluoroacetate and fluorocitrate - which is the chemical created when 1080 is metabolised in the body.

The SMC asked toxicologists to comment on the conflicting reports. Feel free to use these comments in your reporting.

Ian Shaw, Professor of Toxicology, University of Canterbury, comments:

Background on fluoroacetate and fluorocitrate:

"Fluoroacetate (the toxic component of 1080) is very toxic to mammals. It works by inhibiting a key biochemical pathway (the citric acid cycle) which is important in energy generation in cells. If this pathway is stopped the cell dies. Fluoroacetate enters the pathway and results in the formation of fluorocitrate which inhibits a key enzyme in the citric acid cycle. If both fluorocitrate and fluoroacetate are found in tissue samples this is excellent evidence that an animal has ingested and absorbed fluoroacetate. The levels of both determine whether a fatal dose was ingested or not.

"The best samples to analyse for fluoroacetate are muscle and stomach or intestine. The former shows whether the fluoroacetate was absorbed and the latter shows whether it was ingested.

"Fluoroacetate breaks down quite quickly in animal carcases – the higher the temperature the quicker the fluoroacetate breaks down. Since fluoroacetate is very toxic, only low levels in muscle are required to cause death. This means that they might degrade to levels below the level detected by analytical methods. For this reason intestine/stomach levels are useful because they are usually much higher and so don’t degrade below analytical detection methods as quickly as fluoroacetate in muscle samples.

"The analytical results from [Manaaki Whenua] Landcare Research are very reliable; they were carried out in an IANZ accredited laboratory in an internationally acknowledged laboratory that employs excellent scientists. Both muscle and stomach samples were analysed - no fluoroacetate was found. These results are highly credible in my opinion. On the negative side, fluorocitrate was not analysed and the sample size is small.

On the report from the unnamed lab:

"The analytical results released by Flora & Fauna Aotearoa and Clean Green New Zealand Trust are from an unknown laboratory which means that their credibility cannot be assessed. Three rats’ carcasses were analysed including intestines and stomach. No fluoroacetate or fluorocitrate was detected in Rat 1; fluoroacetate and fluorocitrate were found in Rat 2; fluorocitrate was found in Rat 3; fluoroacetate and fluorocitrate were found in Rat 4. A green dye consistent with the colouring used in 1080 pellets was found in Rats 2, 3 and 4.

"The finding that fluorocitrate was present is a little puzzling because this would be expected to be found only in tissues with an active citric acid cycle (e.g. muscle, liver). Intestine and stomach contents would, in my opinion, not normally convert fluoroacetate to fluorocitrate; however, this might be possible by bacteria, particularly in the intestine.

"On the other hand, if the entire stomach and intestine (i.e. not just the contents) were analysed, the cells of these organs might convert fluoroacetate to fluorocitrate. It is not clear from the report exactly what was analysed. If the results are reliable (this is not possible to say since the laboratory and its credentials have not been disclosed) the findings show that the tested animals had ingested fluoroacetate.

"In summary: the Landcare results are reliable, but a small sample and show no fluoroacetate. The other lab results are of indeterminate reliability, but show fluoroacetate and fluorocitrate (the latter is surprising in the context of the tissue analysed). Until we know the identity and credentials of the second laboratory, we can only rely on the Landcare results, in my opinion. The Landcare results might simply show that ingested fluoroacetate had been degraded in the decomposing animals (this is unlikely since there was no fluoroacetate found in the stomach, but cannot be ruled out) or that they had not ingested 1080 from the recent drop."

Declared conflict of interest: I gave a talk at a Flora and Fauna Aotearoa conference on April 6/7, 2019 – this in no way means that I support the group’s views. I understand that Flora and Fauna Aotearoa have reported to the media that I will write a statement to the effect that the laboratory they used for the analysis is appropriately accredited for the work. I agreed to comment on the laboratory’s credentials if Flora and Fauna Aotearoa told me the name of the lab, but they did not. I have no knowledge whatsoever of the laboratory that did the work and thus cannot comment on their expertise in the context of fluoroacetate and fluorocitrate analysis. I am not funded for any work on fluoroacetate.

Dr Belinda Cridge, Department of Pharmacology and Toxicology, University of Otago, comments:

"It has come to light that a second lab has completed a toxicology screen for 1080 in the rats from the West Coast. The results are in direct contrast to the reports provided by DoC earlier in the week and show the presence of 1080 (sodium monofluoroacetate) and its metabolite (fluorocitrate) in the samples. Having seen both reports I have several questions around the processes used in the second (positive) toxicology screen which bring the final results into question.

"Performing the test for 1080, and in particular fluorocitrate, is complicated and requires a very high degree of technical expertise. My understanding is that the laboratory at Landcare are currently the only group in New Zealand who have sufficient expertise and experience with the test to perform the analysis at short notice.

"The method used by the second lab is referenced as Pitt (2015), I couldn’t find a corresponding article for this reference. There are multiple mistakes in the method as presented which may be a simple error but it can’t currently be cross-checked. The fluorocitrate results are presented as being higher than the fluoroacetate levels which is not expected. Additionally, the report shows that the stomach contents were analysed, and there were high levels of the fluorocitrate in the stomach reported, yet conversion to fluorocitrate from fluoroacetate tends to be minimal in this organ."

"For these reasons I am reluctant to fully support the new results until we receive a detailed description of all the methods and controls used by the second laboratory. The results that were published contain several very unusual findings which are in direct conflict with all published studies to date which means that an open and robust scientific discussion needs to take place. We need to determine why such anomalous results may have occurred and assess any further downstream implications."

Declared conflict of interest: I am currently funded to conduct research to develop safer alternatives to 1080 and other pest control poisons. In the close network that is NZ science I am acquainted with, but have not collaborated or worked with, the team at Manaaki Whenua Landcare Research.

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