Monday, December 23, 2013

Arsenic A Global problem

What is Arsenic ?
Arsenic is an element that it is a chemical that can’t be broken down into simpler  chemicals inorganic arsenic is a human carcinogen (EPA, 1984). 
 Arsenic A Global problem
Two Hundred Million people worldwide are at risk to As exposure (NRC, 2001). Several regions in the World are above the WHO’s maximum permissible limit.  These include:
Bangladesh, Cambodia, India, Vietnam, China, Thailand, Argentina, U.S.A, Chile,  Nepal, Mexico, Ghana, Taiwan.

 Where does arsenic come from?
        As occurs naturally & is widely distributed in the Earth’s crust
        Volcanic activity, rock & mineral erosion, & forest fires release As
        As is often concentrated in sulfide-bearing mineral deposits (e.g., gold and copper)
        Strong affinity to pyrite (very abundant) and hydrous iron oxides

Anthropogenic or Man-Made:
        Drilling Wells
        Mineral Extraction
        Processing Wastes
Levels of Arsenic in water depend on:
        Level of human activity
        Distance from pollution sources

The Safe Drinking Water to prevent arsenic

The Safe Drinking Water Act (SDWA) authorizes the USEPA to set national health-based standards for drinking water to protect humans against both naturally occurring and man-made contaminants that may be found in drinking water. US EPA, states, and water agencies/divisions then work together to make sure that these standards are met for rivers, lakes, reservoirs, springs, and groundwater wells.


 Inorganic Forms of Arsenic

  Inorganic arsenic compounds are used to preserve wood
  In the environment, arsenic combines with oxygen, chlorine, & sulfur to form inorganic compounds
  Inorganic forms are toxic

Organic Forms of arsenic

Arsenic in animals and plants combines with carbon and hydrogen to form organic arsenic compounds
Organic arsenic compounds are used as pesticides, primarily on cotton plants
Fish & shellfish can accumulate organic forms  (nontoxic)

Arsenic in the Environment 

Arsenic can only change its form in the environment.  It cannot be destroyed. 
Arsenic in air will settle to the ground or is washed out of the air by rain.
Many Arsenic compounds are easily solubilized in water due to changes in pH and temperature.

How might I be exposed to Arsenic?

Eating food, drinking water, or breathing air containing Arsenic. Breathing sawdust or burning smoke from wood treated with Arsenic.  Living near uncontrolled hazardous waste sites containing Arsenic Living in areas with unusually high levels of Arsenic in rock.

What Are the Final Drinking Water Regulatory Standards for Arsenic?

         The enforceable Maximum Contaminant Level (MCL) is
            - 0.01 mg/L
            -10 micrograms per liter (µg/L)
            - 10 parts per billion (ppb)

Health Effects Due to Arsenic Exposure from Drinking Water

Human Health Effects
Exposure to arsenic in drinking water is reported to cause different human cancer and non-cancer diseases.

Non-Cancer Health Effects

Long-term Arsenic exposure was found to be associated with cardiovascular effects (Utah and Taiwan)
Arsenic exposure has also been reported to cause hypertension, anemia, liver disorders, kidney damage, headache, & confusion.
Among children there have been reports of intellectual impairment when Arsenic in drinking water exceeded 50 µg/L (Bangladesh)
Diabetes Mellitus: Dose-response relationship between Arsenic exposure and Diabetes (Am. J. Epidemiology)
Elevated risk of keratosis and Diabetes as a result of  long-term Arsenic exposure (Bangladesh)

Cancer Health Effects

Cancer: Long-term Exposure (20-40 yrs)
        Skin cancer (Taiwan)
        Keratosis and Hyperpigmentation
        Blackfoot Disease (Mainly Taiwan)
        Lung cancer (Taiwan, Japan, & Chile)
        Bladder cancer (Taiwan, Argentina)
        In a study conducted in the United States no reports of bladder cancer with average 40 µg of As/L in a study
        In a case control study in conducted in Western United States, it was found that smoking can elevate bladder cancer risk when drinking water has As levels near 200 µg/day

Exposure Routes

Arsenic exposure can occur through food, water, air, and medicines
Minimal exposure through air
Major exposure pathway is through diet
Total Food intake : 50 µg As/Day; <4 µg As/day from drinking water

Metabolism of arsenic

Inorganic Arsenic upon ingestion is converted to two “intermediate” compounds that are more toxic than the parent compound  (activation step)
These intermediates are more persistent and are identified in the urine of individuals chronically exposed to Arsenic in drinking water

Inter-individual Variability

Differences in the genetic make up determines whether an individual is susceptible to Arsenic exposure
Differences in susceptibility to Arsenic can be due to differences in age, sex, and nutritional status (e.g. selenium can provide protection against diseases)
Infants and children more susceptible

Benefits of the New Rule

Reducing the arsenic MCL from 50 µg/L to 10 µg/L will help reduce Arsenic exposure to approximately 13 million Americans
Prevent ~19-31 theoretical cases of bladder cancers per year & ~5-8 theoretical cases of deaths due to bladder cancer per year
Prevent ~19-25 theoretical cases of lung cancers & ~16-22 theoretical cases of deaths due to lung cancer per year
Reduce potential non-cancer effects

         Public Health Can Be Severely Impacted by presence of elevated levels of Arsenic in drinking water
        ­in mortality & morbidity
        Everyone is vulnerable
        Degrees of vulnerability depend on
·         Biological susceptibility
·         Exposure & dose
         There Are Safe Levels Below Which No Adverse Health Effects Occur

Take Home Message

         Collectively, we can achieve sufficient reductions to protect public health
         We can limit exposure, especially of susceptible populations
        Pregnant women