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FATE OF LEAD-ARSENATE PESTICIDES IN OLD ORCHARDS 



Peter L.M. Veneman 

 Department of Plant and Soil Sciences 



From the early part of this century until the late 1940's lead- 

 arsenate was used extensively as a general pesticide. This material was 

 applied not only in Massachusetts, but also in any state where apples were 

 being produced prior to the 1950s. In Oregon and Washington the acid form 

 of lead-arsenate was applied, while the basic form was more popular in the 

 Northeast. The amount of pesticide applied may be inferred from old spray 

 schedules, but the exact quantity probably varied from grower to grower. 

 Significant amounts of this pesticide still remain in the soil. Its pre- 

 sence may cause some complications when an orchard site is sold for develop- 

 ment, but even if the site remains in production there is a concern for 

 potential groundwater contamination as well as the possibility that some of 

 the residues end up in the fruit. 



In 1982 we initiated a project at the university to evaluate the fate 

 of lead-arsenate in soils in old orchards, as well as to assess whether or 

 not residues end up in the apple fruit tissue. In this paper we report on 

 our soils studies, while the fruit quality issue will be addressed in a sub- 

 sequent FRUIT NOTES article. 



Our initial study was concentrated at the old university orchard on the 

 Amherst campus. This site has been used for fruit production since the late 

 1800's and has received significant applications of lead-arsenate-containing 

 pesticides, although no accurate records exist as to exactly how much has 

 been applied. We sampled the surface-soil within the old variety block in a 

 grid-like pattern in six rows 1.5 m (5 ft) apart, at 60 cm (2 ft) intervals 

 within each row. The samples were analyzed for lead and arsenic content. 

 Figure 1 shows the spatial distribution of the lead and it is clear that the 

 concentrations are not uniform because prior to the use of modern power 

 sprayers, pesticides were applied to each tree individually with broom 

 sprayers. The large shaded area in Figure 1 shows a region with lead accu- 

 mulations in excess of 400 ug/g (360 lbs/acre). Examination of a 1952 

 aerial photograph confirmed that this area coincided with the spot where one 

 of the small rootstock variety blocks once stood. The other areas with high 

 accumulations of lead were low spots where the spray run-off collected. The 

 spatial distribution clearly indicates a potential problem when sampling 

 these sites. The customary "grab sample" could produce quite different 

 results depending on where a single sample was taken. To avoid such a 

 sampling bias small subsamples at a minimum of at least 20 locations 

 throughout the orchard should be collected, mixed in a clean bag, and then a 

 sub-sample of the mixture sent to a soil testing facility. 



Upon closer examination of the 1952 airphotos it was determined that a 

 very large apple tree had stood just outside the grid sampling area. We 

 sampled the upper 10 cm of the surface soil of that area along a transect 

 across the approximate tree location. The results showed high concentra- 

 tions of lead and arsenic (1400 and 340 ug/g, respectively) where the 

 dripline must have been. Elevated levels (700-800 ug/g lead) were observed 

 within the periphery of the former crown, while much lower values (200-300 

 ug/g lead) were found outside the former dripline. It is interesting to 

 note that even decades after removal of the trees these patterns still 

 remained quite distinct. 



