Comparison of Bifenthrin Formulations for Their Skin and Eye Irritation Potential Using the Pollen Tube Growth Test
S Millward, P Lobb
The Pollen Tube Growth Test (PTGT) is an effective screening method for measuring the potential of a chemical formulation to affect living cells. The PTGT has been compared against other types of testing, and it shows a good correlation with, for example, the Draize rabbit eye test and the human skin patch assay. It measures the EC50, which is the effective concentration at which 50% growth is observed compared with a control. Results are expressed in parts per million (ppm). A highly toxic formulation will have a very low EC50 value while a less toxic formulation will have a higher EC50 value. Zelam has used the pollen tube growth test to determine the relative toxicities of different bifenthrin formulations. Bifenthrin is regarded as a low toxicity insecticide, but some individuals can become highly skin sensitive to it. A condition called paresthesia results, which is a burning sensation in the skin, accompanied by rashes or redness that can last for up to 12 hours.To conduct a PTGT, a pollen grain suspension in growth medium is mixed with various concentrations of a test formulation, and incubated for 18 hours in the dark. The resulting pollen tubes are stained using a blue dye, the unbound dye is washed out and the bound dye re-dissolved by lowering the pH. The mass of pollen tubes is then represented by the amount of dye, and this is then determined by the absorbance of light at 607nm. Using this data one can plot a graph of pollen tube growth vs concentration, and then derive the EC50 value.
The present results show an emulsifiable concentrate formulation has a very low EC50 value of 15ppm indicating a high potential to cause sensitization. A suspension concentrate formulation has an EC50 value of 220ppm, which indicates much less potential to cause sensitization. In comparison, the encapsulated formulations developed have shown even higher values with an EC50 of 3,500ppm.