Reduction of Arsenic in groundwater by filtration systems

10 μg/L is the Maximum Contaminant Level (MCL) for Arsenic in water for drinking purposes, according to the Environmental Protection in 2001  (EPA ). Arsenic is a naturally occurring metal highly toxic to all life forms and classified as a group 1 human carcinogenic substance by the World Health Organization ( WHO ). Commonly found in metasedimentary bedrock reservoirs used as a supply for drinking water. The EPA mandate was approved after relinquishing the former enforceable standard of 50 μg/L for arsenic in community water systems under the National Interim Primary Drinking Water Regulations. And furthermore, the states of New Jersey and New Hampshire have established the safest and most rigorous MCL of 5 μg/L.

In the United States alone, more than 3 million people are directly affected by the distribution of water that contains a concentration of arsenic above the MCL of 10μg/L  (Barnaby et al., 2017) .

This map of the United States in figure 1 shows the estimated number of people that are affected by arsenic in their drinking water. North West, Midwest, and New England are the regions with the most estimation of people being affected by arsenic. More specifically, the state of Maine collects its groundwater supply from wells in metasedimentary bedrock units that are considered to be contaminated with high concentrations of As, with nearly 30% of these wells being polluted with higher Arsenic concentrations than the MCL (Ayotte., 2003).

The state of Maine provides data for the different concentrations in the groundwater in private wells, mainly focusing on As. The link above provides different data regarding private well ownership, testing behavior, and water quality for the state of Maine; the data can be modified and shown in tables, charts, trendlines, and maps while distributing the data in counties or towns.

  The history of MCLs: 

Ingesting extremely elevated doses of arsenic can develop acute arsenic poisoning, the immediate symptoms include vomiting, abdominal pain, and diarrhea.

Chronic arsenic poisoning occurs after a minimum exposure of approximately five years, and it may be a precursor to skin cancer. The first symptoms usually appear first in the skin, this includes pigmentation changes, skin lesions, and hyperkeratosis (hard patches on the palms and soles of the feet). Additionally, a person with chronic As poisoning can also develop cancer in multiple internal organs: bladder, kidneys, and lungs are the main organs affected by cancer caused by arsenic. Nonetheless, cancer is not the only result of prolonged exposure to As in the water. It can also cause developmental effects, diabetes, pulmonary disease, and cardiovascular disease.  (WHO, 2016) 

Arsenic poisoning during pregnancy directly affects the child's health; creating an increase in mortality in young adults. Multiple cancers, lung disease, heart attacks, and kidney failure are the main causes of mortality. Arsenic also affects children's cognitive development, intelligence, and memory (Tolins et al., 2014).

STAND WITH US AS WE STAND AGAINST HARMFUL TOXIC CHEMICALS.

Defend our Health is an organization in Maine that focuses on reducing the exposure of harmful chemicals like arsenic and PFAS from the water and food. More specifically, they focus on strengthening the health standards for drinking water. Their aim is to reduce the current MCL of 10 μg/L, to the levels of New Jersey and New Hampshire of 5 μg/L, which has been scientifically proven to reduce the threshold exposure to this harmful chemical.

To subscribe to their campaign click  here .

Thirty-two private wells in Mount Desert Island, mainly in Bar Harbor and Mt. Desert, and a few in Trenton were used to collect the samples. The samples were collected over a series of years, during free and optional private well water testing events:

Monthly samples: During June 2020 - August 2021, 18 private well owners participated in a monthly sampling study where well owners collected samples pre- and post-filter near the 28th day of each month. Due to scheduling errors, some owners have missing data for a few months.

Particular events: 14 private well owners participated in an opportunistic sampling event during 2016-2021 which also included both a pre- and post-filter sample collected at the same day/time. 

The maximum As concentration in the groundwater was used to distribute the 32 wells in this pie chart. Almost half of all wells presented levels of As already below the NJ and NH MCL of 5 µg/L. Similarly, ~70% of wells in our study already had levels below the current federal MCL of 10 µg/L, whereas ~30% had to require a filtration system to reduce to safe levels. Ultimately, the higher As levels are in groundwater the higher the risk of contracting arsenicosis due to chronic exposure, and 2 wells exceeded the former MCL of 50 µg/L, putting them at a higher risk.

The reduction of elements by the R.O. system suggests that this system is effective not only to reduce As, but also to reduce other elements. In this case, uranium, manganese, iron, and lead were analyzed alongside arsenic, in order to evaluate the elimination of these chemicals. Expanding on As, Mn, and U, we identified that R.O. systems can successfully reduce levels of As below the MCL and levels of U below the U MCL of 30 μg/L.

The data has been fitted with a power-law trendline where the exponent of the equation represents the slope of the line, the percentage of the element removal by the filter. The top figure compares the different removal percentages between arsenic, uranium, and lead. Arsenic and uranium both have a high R² value; ~13% of arsenic is removed by the particulate filter, either as solids or adsorbed by a trapped solid. A study done in New Jersey and Maine suggested that the failure rate in households without particulate filters are similar to those with particulate filter; particulate filters alone do not contribute drastically to the removal of arsenic in groundwater (Yang et al., 2020). Uranium was not removed by the particulate filter; most of the uranium seems to be dissolved in the water rather than in a solid or adsorbable phase.

The trendline for lead does not represent a good fit (R²) of 0.04; the particulate filter is not systematically removing the metal. The average concentration of lead for unfiltered samples experienced an increase of 17.2% after going through the filter. This lead increase is likely related to lead being released by the household pipe system. Iron too reveals a poor fit (R²= 0.05), and thus it is systematically removing iron. The concentration of iron in groundwater varies extensively throughout the wells in this study and also temporally throughout the year. The particulate filter experiences very different Fe concentrations per household. One well in this study (Well 8) hosted 223 µg/L of iron in their unfiltered groundwater, whereas once filtered it had a concentration of 503 µg/L, this increase of 125% more Fe in water may be attributed to the accumulation of iron hydroxides in the particulate filter. In this case, the well owner should replace the particulate filter more frequently because the accumulation of iron solids in the filter has caused iron particles to leech through the filter and into the water. 

As is not the only element of concern presented in groundwater, hard water, bacteria, radon, uranium, and many other contaminants can affect the quality of our drinking water. For instance, a water softener aims to filter high concentrations of magnesium and calcium from hard water and to reduce the stain and traces left from dishes and clothing because hard water inhibits the effectiveness of soaps and detergents (Sharjeel et al., 2018).  Ultraviolet water treatment systems would not considerably reduce metals, as their main purpose is to reduce and kill bacteria from the drinking water by using UV wavelengths to dissociate the DNA on living cells, a clear example of this is the reduction of E. coli by UV (Frank et al., 2014). And lastly, radon gas is produced by the breakdown of uranium and it produces lung cancer after chronic exposure, EPA recommends aeration devices or a Granulated Activated Carbon system to successfully mitigate radon gas from the groundwater (EPA, 2014).

Image 1 shows how well these types of filters reduced Fe, but it is also worth mentioning that the reduction can be attributed to the elimination of suspended solids, Iron hydroxides, by the particulate filter installed before the Water Softener, or UV. Thus, we can argue that these systems do reduce the Iron concentrations when a particulate filter is also installed. Similarly, it successfully reduces concentrations of lead and manganese from the groundwater, showing all filtered dots below their unfiltered counterparts.

Image 2 shows a better perspective for the concentrations of arsenic and uranium. For these two chemicals, the reduction of their respective concentration varies throughout the graph, but it does not drastically reduce As or U. In fact, well G and N1 presented higher concentrations of As after passing through the filter. We know that these types of water treatment systems are not meant to reduce As, but meant to reduce other contaminants, and thus if the chemical is being added by the filter, it would mean that a replacement is needed. Similarly, well C and M resulted in higher uranium concentrations after the water passed through the filter.

Ultimately, this study concludes that R.O. systems were the most effective to remove As from the groundwater and to remove all elements assessed in this study, ~99% in both cases. Also, well owners with high arsenic and elemental concentrations tended to choose R.O. systems for their house as a water treatment system. While these systems work well to remove all arsenic, they failed to reduce As concentrations when the filter had not been replaced. Thus, the first step for a well owner to eliminate As exposure through groundwater is to choose an adequate water treatment system, like RO, and the second step is to properly maintain the treatment system. Finally, well owers should regularly test their well, potentially multiple times per year to look for annual variations.  R.O. systems reduced the water to levels below the ME MCL of 10 μg/L, and below NJ and NH MCL of 5 μg/L regardless of the groundwater variability over the seasons. Therefore, in case the state of Maine approves a reduction to the MCL to 5 μg/L, R.O. systems will allow well owners to stay below the MCL and prevent ~99% of exposure to the As in the groundwater.

Synopsis:

Half of the population in Maine rely on private wells as their biggest source of drinking water, and almost ~25% of the population rely on private wells that are yet to be tested. Not knowing the chemistry in the groundwater can be dangerous, because you are not sure what are you exposed to in your water. Arsenic is a colorless, odorless, colorless element, basically invisible in water, and thus testing should be encouraged more. Zheng (2017) states as optimistic bias as perceiving real risks lower than what they objectively are, and thus As is considered by some private well owners as less harmful. This optimistic bias leads to a lack of testing and engagement to solve the real and harmful issue.

I believe that in order to present the real risk of this harmful substance, we would have to visually demonstrate the real impact that each MCL has and how the reduction of As concentration benefits the well owner. In order to gather this information, this study compresses different research papers that focus on the impact arsenic has on our drinking water. Similarly, the human effects caused by arsenicosis were taken from different organizations that had previously studied arsenic and its impacts on the human body, like WHO and the National Research Council.

For us to successfully assess the effectiveness of different mitigation systems in MDI, we had to gather information from wells that differed in the water treatment system. Each type of filter was studied in the same way, first by setting the element concentration in unfiltered samples, and then compare to the concentration after the water has passed the filter. Each type of filter was presented, describing the purpose and the benefits that each has, but in the focus of this study, they did not reduce As to levels that are benign to the human body. Therefore, after our data showed how reliable R.O. systems are to reduce As and other harmful contaminants, our goal became to demonstrate that it is effective and that people with elevated As in their groundwater should consider changing to a more effective mitigation system.