Soil at many cattle tick dip sites is contaminated due to past use of arsenic and DDT.
Arsenic was used as the tickicide in the dip solution up until 1955 when the ticks became resistant to it.
DDT, an organochlorine (OC) was then used until it too became ineffective in 1962. Since 1962 other much less persistent tickicides have been used to dip cattle.
Arsenic and DDT can still be found at high levels in the soil beside many dip baths today because they are very persistent compounds.