Pica Behavior and Contaminated Soil

What's the Problem?

Pica behavior is the craving to eat nonfood items, such as dirt, paint chips, and clay. Some children, especially preschool children, exhibit pica behavior. Pica behavior is most common in 1- and 2-year old children and usually diminishes with age so that elementary-age children seldom exhibit pica behavior. Soil ingestion is the consumption of soil resulting from various behaviors including, but not limited to, mouthing objects or dirty hands, eating dropped food, and intentionally consuming soil. All children (and even adults) ingest small amounts of soil daily from these behaviors. The distinguishing factor for soil-pica is the recurrent ingestion of unusually high amounts of soil either intentionally by eating dirt or unintentionally from excessive mouthing behavior or eating dropped food. While the typical child might ingest 1/8 teaspoon soil daily (or about 100 to 200 milligrams), children with soil-pica behavior ingest about a teaspoon or more of soil daily (or about 1,000-5,000 mg or more per day).

Pica and specifically soil-pica is a public health issue that has gotten little attention because people do not realize that it can lead to significant exposure to chemicals. However, soil ingestion has already been shown to be a significant risk factor for increased blood lead levels (BLL) and for exposure to soil-transmitted parasites. Up to 20% of preschool children have soil-pica behavior, which parents may not notice since their preschool children may play unattended in the safety of their back yards.

In addition, pica behavior has also been observed in adults, and in particular pregnant women. In many cases of adult pica, the practice has cultural significance or is the result of craving during pregnancy. In some cases, the craving is due to a nutritional deficiency, such as iron-deficiency anemia.

An example of an element that may be found in soil is arsenic. Inorganic arsenic doesn't degrade and binds to soil particles at the surface. Historically, repeated applications of arsenic-containing pesticides and herbicides may have increased arsenic levels in top soil to very high concentrations and can be a potential problem for children with soil-pica behavior. Pesticides containing arsenic are no longer commercially available. However, in many cases, soils were treated decades ago, yet the arsenic remains at the surface increasing the risk of contact from children's play activities. If soil ingestion is suspected among children, it is important to know (1) the amount of soil ingested, (2) the frequency of ingestion, and (3) the type of material ingested.

Who's at Risk?

Groups at risk of soil-pica behavior include children aged 6 years and younger as well as individuals of any age who are developmentally delayed. Soil-pica behavior is highest in 1- and 2-year-old children and declines as the children grow older.

Can It Be Prevented?

Parents and guardians must be responsible for closely monitoring young children and persons who have developmental delays to ensure that soil is not ingested. Additionally, proper hand-washing techniques must be employed after being outside and before eating to ensure that contaminants and parasites in soil do not pose any further threats through hand-to-mouth contact.

The Bottom Line

Soil-pica is the ingestion of soil which may lead to exposure to chemicals and has been shown to be a risk factor for exposure to lead and soil-transmitted parasites. Up to 20% of preschool children have soil-pica behavior, often consuming soil in their own backyards. Pica behavior can pose significant risks and should be minimized so that those at risk are not harmed by contaminants in the ground. Parents should monitor children when they are playing in the yard and should enforce hand-washing after playing outdoors and before eating.

Case Example

Arsenic Case Example

This scenario takes place in the mid-west (Omaha, NE, for example), which has alkaline soil and low rainfall, two factors that promote binding of arsenic to soil particles. In these conditions, arsenic will bind with the top few inches of soil, so the surface soil usually has the highest arsenic levels and concentrations decrease with depth. A preschool child develops nausea, stomach cramps, vomiting, sore throat, listlessness and mild diarrhea, so the mother takes the child to the emergency room. Doctors treat him for symptoms but are unable to identify a cause. The child is admitted overnight for observation and recovers. Two weeks later, mother and child are back in the hospital with the child experiencing the same symptoms. Again, the child is admitted overnight, recovers and is sent home. A week later, mother and child are back a third time with the child displaying the same symptoms. This time the doctor notices periorbital swelling (swelling around the eye socket). This reminds her of an incident in Japan in the 1950s when people who were exposed to arsenic by consuming contaminated soy sauce displayed the distinguishing characteristic of periorbital swelling that subsided shortly after exposure. The doctor tests the child for total arsenic in the urine and finds 500 ppb. Since the average total arsenic levels in urine is 7 ppb (and the 95th percentile for children is 47 ppb), this level is considered very high. The doctor explains that arsenic is excreted rapidly from the body via the urine and that the urine arsenic level from the previous day was probably much higher. The doctor asks the mother if the child has eaten any type of seafood within the last 3 days. Seafood will result in high arsenic levels, although arsenic in seafood, known as "fish arsenic" (arsenobetaine), is not toxic. The mother replies that the child has not eaten any seafood.

The doctor asks the mother about possible pesticide exposure, but she says that pesticides are kept behind child proof cabinets or in the free-standing locked garage that is used as a storage area. The doctor suspects "Munchhausen by proxy," a condition where a parent or guardian will poison a child or relative so he/she will require diagnostic tests and hospitalization. Before she investigates this possibility, she asks the mother if the child has any unusual eating habits. The mother remembers catching him eating a cigarette butt about a year ago, but she reprimanded the child and has not seen the behavior since.

The doctor refers the child and mother to a case worker who visits the home to observe the home environment and the child's behavior. The case worker watches the child playing in the back yard and notices that he is surreptitiously eating dirt. The mother is quite surprised at this behavior and very apologetic. The soil is then tested and found to contain 1,000 ppm of arsenic. The parents do not know how the arsenic got there but state that the house was built on the site of an old apple orchard that was owned by the child's grandparents. In talking to the grandmother, they find that she regularly used a pesticide in the apple orchard. The doctors research the pesticide and discover that the main ingredient is arsenic trioxide. Remaining in the soil all these years, the arsenic has been causing the child's symptoms.