Risk management strategies based on experience from nitrate toxicity case study.

Curseu, Daniela ; Popa, Monica ; Sirbu, Dana 等

1. INTRODUCTION

The nitrate ion (N[O.sub.3.sup.-]) is the stable form of combined nitrogen for oxygenated systems. Although it is chemically unreactive, it can be microbially reduced to the reactive nitrite ion. Nitrite converts oxygen-carrying hemoglobin to methemoglobin, which cannot bind oxygen, by oxidizing the [Fe.sup.2+] in heme to [Fe.sup.3+]. The condition of methemoglobinemia is characterized by cyanosis, stupor, and cerebral anoxia. Naturally, 0.53-3.0% of the total hemoglobin (Hb) circulates as methemoglobin (MetHb). Generally, detectable clinical signs of methemoglobinemia appear at 10% MetHb (Brunning-Fann & Kaneene, 1993; Kross et al., 1992).

The aim of this study was to evaluate reported cases of infant methemoglobinemia in relation with environmental exposure to nitrate, in favor of appropriate intervention programs of risk management in Cluj County, Romania.

2. MATERIAL AND METHOD

To satisfy our objective, infants diagnosed with methemoglobinemia at the pediatric emergency departments from Cluj County, Romania, between 2002 and 2006 were identified. For each case, the following data were recorded: date of admission to the emergency department, age, sex, weight, place of residence, reason for consultation and associated symptoms, feeding characteristics in the last days, foods ingested in the previous 24 hours, results of laboratory investigations.

Water samples as well as fruit and vegetables cultivated in individual farms and used for infant's feeding, were collected 2 days after the infant was hospitalized. The nitrates/nitrites concentration was analyzed using the phenol-disulphonic acid method, respectively the sulphanilic acid and [alpha]-naphtylamine hydrochlorate method. In addition, information on household environmental conditions (including drinking water hygiene, sanitation and domestic hygiene) were provided.

3. RESULTS AND DISCUSSION

During a five years period (2002-2006), in Cluj county have been recorded 28 hospitalised cases of methemoglobinemia (42.9% boys and 57.1% girls).

The average age was 45 days, with a range of 12 days to 6.5 months. The majority of cases (79%) were under 4 month.

Annual data for live births in Cluj County were also available, so we were able to calculate the incidence rate of methemoglobinemia based on clinically reported cases (Table 1). The annual estimated incidence of methemoglobinemia ranged from 42 to 239 per 100000 live births during the study period, with a mean of 118/100000 over the five year period. Although these 28 cases are not representative for the entire population of Romania, the rates are in accordance with the incidence rates earlier reported by Ayebo et al. (1997) in contiguous areas from Transylvania.

A summary of selected clinical data is presented in Table 2. The average birth weight of infants was 2921 [+ or -] 422 g, which is above the 2500 g, internationally acceptable definition of low birth weight, but statistically (p<0.001) lower than the Romanian national average of 3465 [+ or -] 365g. The average weight of infants at the time of diagnosis with methemoglobinemia is 4020 [+ or -] 450g, significantly lower than comparable age group infants (4020g vs. 4980g). Breastfeeding data indicate that about 74% of infants had been breast fed for at least one week postpartum. The duration of breastfeeding was generally less than one month. No infant was diagnosed with methemoglobinemia while being breast-fed.

Medical examination revealed a high incidence of anemia in infants reported with methemoglobinemia. The hemoglobin of infants averaged 11.2 g/dL for all ages, which is within the normal range of Romanian national hemoglobin values of 10.8-18.0, with a mean of 13.3 g/dL. However, when compared to national average data according to age distribution, 11 cases (39.2% of the infants) were classified as anemic (Table 3). This observation is important because the anemia emphasizes the anoxia status. Thirty-one percent of the infants had symptoms of diarrhea on initial diagnosis, and all cases presented cyanosis.

Geographically, all infants hospitalized with acute methemoglobinemia lived in rural and received their drinking water from private wells. Another important area of concern was well-water sources, well depth, the level of well-water nitrate (mg/L), and boiling of liquids. Findings in this study indicate that all communities where methemoglobinemia was reported had nitrate levels above of allowable limit of 50 mg/L. The highest recorded concentration was 265 mg/L. Well construction methods, placement, and general hygiene were primary causes of poor well water quality and high nitrate level. The most wells were dugouts of less than 8 meters, with some as shallow as 3 to 4 meters, without casing and no protective cover over the wellhead. Also, the wells were located very close to human traffic areas and livestock rearing facilities. Moreover, household laundry and washing of utensils is done around the open shallow well head. Nitrate contamination from agricultural use of fertilizers and animal manure may occur, but the most likely source of nitrate for the wells observed in this study is local human and animal waste.

The infants were weaned completely after a short breastfeeding period to cow milk diluted (1:1) with boiled water. All mothers interviewed routinely boiled water to kill pathogenic microorganisms in well water before use for infant feeding. However, this practice actually increases nitrate concentration.

No reported episodes of methemoglobinemia occurred within the rural communities with normal nitrate well water levels or in urban population supplied with treated tap water. According to the well water nitrates concentration, we categorized two groups at risk of methemoglobinemia:

--moderate risk--well water pollution between 50-100 mg/L;

--high risk--well water pollution above of 100 mg/L.

A significantly higher mean value of methemoglobin was found when nitrate concentration in well water exceeded 100 mg/L (Table 4).

Nitrites were detected in concentration up to 0.25 mg/L in all samples of well water.

In one multiple episode of methemoglobinemia reported the first episode occurred when mother offered some tea to her baby, and the repeat episode was when infant's feed included spinach, carrot and apple juice. They are given to supplement the infant's diet of diluted cow milk.

Frequently the fruits and the vegetables cultivated in individual farms constitute an additional source of nitrates. Table 5 shows the nitrates and nitrites average concentrations in vegetables comparing to maximum allowable level (MAL) according to Direction 975/1998 of Romanian Ministry of Health.

It has to be noted the over limit nitrates concentrations in potatoes and carrots samples. This observation is important because carrot soup is often recommended if the infant is suffering from diarrhea, so the high nitrate level in carrots and gastrointestinal illness go "hand in hand" for bacterial conversion of nitrate to nitrite in the stomach. For this reason many other studies associate methemoglobinemia with infantile cases of severe diarrhea (Hanukoglu & Danon, 1996). Also, others authors suggested that bacterial growth within the bottle or stored homemade soup / purees of mixed vegetables and exogenous conversion of nitrate to nitrite is possible the source of the problem (Echaniz et al., 2001; Fewtrell, 2004).

4. CONCLUSIONS AND RECOMMENDATIONS FOR RISK MANAGEMENT

1. The greatest risk of methemoglobinemia occurs in infants less than 4 months bottle-fed with diluted cow milk or formulas prepared with nitrate-contaminated water from wells.

2. Well construction methods, placement, and general hygiene are primary causes of poor well water quality and high nitrate levels. All prenatal and well-infant visits should include questions about the home water supply. If the source is a private well, the water should be tested for nitrate.

3. Since many vegetables are high in nitrate, consumption of home-prepared infant foods from vegetables (spinach, potatoes, carrots) should be limited until the infant is 4-6 months old.

4. An educational program for mothers to increase duration of breast feeding could be a very effective method of preventing infant methemoglobinemia.

5. REFERENCES

Ayebo, A.; Kross, B.; Vlad, M. & Sinca, A. (1997). Infant methemoglobinemia in the Transylvania region of Romania. Int J Occup Environ Health. 3(1): 20-29, ISSN 1077-3525.

Brunning-Fann, C.S. & Kaneene, J.B. (1993). The effects of nitrate, nitrite and N-nitroso compounds on human health: a review. Vet Hum Toxicol. 35(6): 521-538, ISSN 0145-6296.

Echaniz, J. S.; Fernandez, J. B. & Raso S. M. (2001). Methemoglobinemia and Consumption of Vegetables in Infants. Pediatrics. 107(5): 1024-1028, ISSN 1098-4275.

Fewtrell, L. (2004). Drinking-Water Nitrate, Methemoglobinemia, and Global Burden of Disease: A Disscussion. Environ. Health Perspect. 112(14): 1371-1374, ISSN 0091-6765.

Hanukoglu, A. & Danon, PH. (1996). Endogenous methemoglobinemia associated with diarrheal disease in infancy. J Pediatr Gastroenterol Nutr. 23:1-7. Available from:http://pediatrics.aappublications.org/cgi/reprint/107/5/ 1024 Accessed: 2008-04-02.

Kross, B.C.; Ayebo, A.D. & Fuortes, L.J. (1992) Methemoglobinemia: nitrate toxicity in rural America. Am Fam Physician. 46(1): 183-188, ISSN: 0002-838X.

Tab. 1. Incidence of methemoglobinemia in Cluj County.

Year Cases Live births Incidence rate *

2002 12 5,021 239
2003 2 4,890 42
2004 3 4,795 63
2005 6 4,673 128
2006 5 4,334 115
Total 28 23,713 118

* Number of cases per 100,000 live births

Tab. 2. Clinical data of hospitalized infants

 Mean/ [+ or -] SD Mean/ [+ or -] SD
 (range) (1) (range) (2)

Birthweight (g) 2921 [+ or -] 422 3465 [+ or -] 365
 (2200-4105)

Weight at admission (g) 4020 [+ or -] 450 4,980 [+ or -] 365
 (3300-6750)

Breastfeeding (days) 28 (10-45) NA (3)

Hemoglobin (g/dL) 11.2 [+ or -] 1.5 13.3
 (6.8-13.1) (10.8-18.0)

(1) N=28 cases; (2) Romanian National Average; (3) not available

Tab. 3. Comparison of infant hemoglobin levels

 Anemia cases Cases of National
 methemoglobinemia average Hb
 Hb (g/dL) (g/dL)

Age N Mean (range) Mean (range)
(month)

under one 2 11.3 16.6
month (11.1-11.7) (13.2-23.0)

1-4 month 8 11.0 13.3
 (7.5-12.5) (10.8-18.0)

over 4 1 11.2 12.4
month (9.6-14.7) (10.2-15.0)

Tab. 4. The average values of methemoglobinemia in relation
with nitrate levels in well water

Nitrate level 50-100 mg/L

Values of N Mean [+ or -] SD
MetHb (%)
 10 12.1 [+ or -] 2.5

t-test (p-value) t=4.67 (p=0.0001)

Nitrate level >100 mg/L

Values of N Mean [+ or -] SD
MetHb (%)
 18 17.2 [+ or -] 2.9

t-test (p-value) t=4.67 (p=0.0001)

Tab. 5. The nitrates and nitrites average concentrations in
vegetables

 Nitrates Nitrites
 concentration concentration
 (mg/kg) (mg/kg)

Species Mean [+ or -] SD MAL Mean [+ or -] SD

carrots 395.9 [+ or -] 23.3 400 0.45 [+ or -] 0.09
potatoes 311.3 [+ or -] 37.01 300 0.78 [+ or -] 0.27
spinach 291.7 [+ or -] 69.4 2000 0.58 [+ or -] 0.12
squash 48.5 [+ or -] 11 60 0.32 [+ or -] 0.05