This particular quote is used within the "chemtrail" community, a segment of which believes that the long white trails seen behind planes (contrails) contain unusually high amounts of aluminum. Some of them test their soil, and if it's above the level of 400 ppm, then they claim that's evidence of aluminum being sprayed. The original source for this usauge of the quote is: http://www.holmestead.ca/chemtrails/soiltest.html The source is given as A&L Canada Laboratories East, and indeed a search of their web site seems to support it: http://www.alcanada.com/index_htm_files/Calcium Nutrition in Plants.pdf http://www.alcanada.com/index_htm_files/Factors Effecting Specific Gravity in Potatos.pdf And yet they also (correctly) say: http://www.alcanada.com/index_htm_files/Metal Concentrations in Natural Soils.pdf So, if a common range of aluminum is 10,000 to 300,000, then how exactly can 400 be toxic? Clearly something is not right here. It turns out the 400 ppm figure is NOT the level in the soil that's toxic, it's the level IN THE PLANTS THEMSELVES: http://aesl.ces.uga.edu/publications/plant/Nutrient.htm But then, to cloud the issue, we find this: http://www.soilminerals.com/soiltest_page1.htm So what are they talking about? Soil is usually AT LEAST 10,000ppm aluminum. You might think they are discussing "available aluminum", Al3+, which is the aluminum dissolved in acid soils. However, Al3+ (or Al+++) is toxic at 0.5ppm. Perhaps they have confused thier units, and actually mean ppb (parts per billion) not ppm (parts per million). Clearly though the quote is wrong. I suspect it might refer to the results obtained from some other type of test, like one using a Kelowna extraction solution, or the Mehlich 3-Al test. But I'm not really familiar with them.