Arsenic in wells potentially reflects past pesticide use on orchards

Until the 1950s orchards were heavily fortified with lead arsenate-based pesticides to keep the bugs at bay, and scientists have found that this arsenic is still lingering. 

Arsenic and orchards 

By the 1930s, Connecticut was once host to up to 47,000 orchards, and until the 1950s orchards were heavily fortified with lead arsenate-based pesticides to keep the bugs away. These arsenic-based chemicals were eventually banned because of their potential for harmful effects on humans.   

Despite the fact it has been more than half a century since lead arsenic pesticide was used to dowse Connecticut fruit trees, the poison still lingers in the ecosystem. Many of those orchards have since been converted into residential and commercial properties, but research conducted by scientists at both the University of Connecticut (UConn) and Eastern Connecticut State University (ECSU), found a strong correlation between arsenic contamination and proximity to those historic orchards; the closer the well is to those locations, the greater the probability of finding arsenic there. 

The project 

Gary Robbins, UConn professor of geosciences and natural resources, explains the study into arsenic remnants started with a request from the state Department of Energy and Environmental Protection (DEEP) in 2013. Robbins and his research group, including Mark Higgins (21 Ph.D.) and Meredith Metcalf (13 Ph.D.), study groundwater contamination and work to trace the source of contaminants.  

Robbins and his team were asked to survey wells for arsenic in eastern Connecticut, starting with Lebanon. Metcalf fronted the project and collected water samples from hundreds of homes residing in the eastern half of the state. Many of these locations served as the starting point for Higgins’ Ph.D. dissertation research that involved analysis of over 100 wells and 189 orchards, which included soil samples to determine the presence of lead and arsenic.  

“After sampling, we looked at the distribution and possible sources of arsenic that caused the groundwater contamination, because a significant percentage of wells were contaminated and many of those were above the EPA (Environmental Protection Agency) drinking water standard,” Robbins said. “The issue that came up is, where is this all coming from?” 

The researchers speculated that the arsenic-rich geologic formations could be the culprits, and could explain where the arsenic was coming from, as a closer look at the distribution of the wells offered no explanation to the presence of the substance. However, the scientists conducted further analysis and investigated the historic uses of arsenic. This revealed that arsenic-based pesticides were widely used from the late 1800s until the 1950s, when dichlorodiphenyltrichloroethane (DDT) became a popular alternative.  

“These pesticides would be sprayed on all fruit trees to kill the pests like gypsy moths up to six times a year in some cases,” Higgins said.  

Tens of millions of pounds of arsenic-based pesticides were applied every year in the US, and although the lead arsenate pesticides fell out of popularity and were banned in some states starting in the 1950s, it was not until 1988 that they were officially prohibited throughout the entirety of the US.  

“Heavy application rates, coupled with the fact that lead and arsenic can travel quite slowly through the ecosystem, is a combination that makes for long-lasting remnants of the poisons,” said Higgins. 

Determining the source of contamination 

As part of their research, the team collected soil cores down to three feet at the orchard sites: “We found high levels of arsenic persisting, more than one would expect for 50 to 60 plus years after these pesticides were applied. It is unlikely that they’re migrating downward into the water anymore and are probably immobile.” 

This added complexity to definitively determining the source of the contamination, despite the strong proximity correlation. Higgins commented, “recent studies show certain compounds like phosphate-containing fertilizers are changing environmental conditions and can start mobilizing previously immobile contaminants in the soil.” 

The scientists found evidence of leachability of the contaminants in some soils. Robbins determined that future steps will be to look at the age of water through tritium testing, because under some conditions, like bedrock and glacial till commonly found in Connecticut, water can move through soil and rock extremely slowly, and this impacts how contaminants enter the groundwater supply. Dating that water will help determine if today’s results of arsenic are the result of the application of pesticides decades ago, or the result of more recent activities. 

“In other areas of the state, domestic wells are both near historic orchards and arsenic-rich geologic formations,’ explained Higgins, “and this poses additional challenges to determining the source of the contamination. 

“How do we definitively say the contamination came from one or the other or both? We need these additional lines of evidence. With this paper, we have a strong dataset as far as the numbers of orchards. With additional funding and data from a larger area, I think it will be telling of whether it’s coming from the orchards or not, and how it is getting into the wells.” 

The researchers noted that though many sanitarians in these localities are aware and do tell people to test their wells, state guidance lists arsenic as something that is not required to be tested for, instead recommending testing every five years. The researchers highly recommend testing domestic wells for arsenic and say the state guidelines are likely to change. 

“It is important for people in these areas to know, because arsenic at these concentrations is not something that will make you sick tomorrow or in 10 years. But if you’re drinking this low-level arsenic for 30 years, there are likely health risks from chronic exposure to this known carcinogen. 

“I think that arsenic will become part of the routine water quality testing soon enough,” Robbins concluded. 

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