Arsenic in the drinking water of the city of Antofagasta: epidemiological and clinical study before and after the installation of a treatment plant.

This is a second report of epidemiological and clinical investigation, related to the arsenic health problem, unique in the world, occurring in the city of Antofagasta, Chile. The arsenic problem originates in the chronic contamination of water supply in the city during 12 years. This phenomena, investigated clinically and epidemiologically and first reported in 1971, prompted the installation of a water treatment plant. This report aims to evaluate the working efficiency of the plant. The study was carried out through the examination of arsenic content in hair and nail clipping samples of the inhabitants of Antofagasta and the determination of this element in cultivated vegetables and carbonated beverages. Also a clinical study in school children, looking for cutaneous lesions attributed to arsenicism, was made. Results are encouraging. They reveal that contamination persists but in significantly lower levels.


Introduction
Antofagasta, a city of 130,000 inhabitants, received a water supply containing high quantities of arsenic (0.8 ppm) between 1958 and 1970. The source of the high arsenic content water was the Toconce River, whose waters come from the Andes Mountains at an altitude of 3000 ms and are brought over 300 km to Antofagasta.
At the beginning of the 1960's the first dermatological manifestations were noted, especially in children (Table 1). Several systemic cases attributed to arsenicism (bronchiectasis, Raynaud's syndrome and other peripheral vascular phenomena, ischemia and myocardial infarction, mesentheric thrombosis), including a few fatal ones were sent to Santiago's hospitals. *Servicio Nacional de Salud, Ministerio de Salud Publica, Republica de Chile, Santiago, Chile.
The magnitude and the interest of the problem motivated sanitary authorities to carry out a complete study. The prevalence of cutaneous lesions attributed to arsenicism in the general population August 1977 and arsenic content in hair, nail clippings, and urine samples, were determined for inhabitants of Antofagasta and Iquique. The latter city did not have an arsenicism problem and was used as control group (Table 2). Also determinations of arsenic in water and carbonated drinks were made in Antofagasta. Measurements of arsenic in water drinks revealed values between 0.6 and 0.8 ppm. Carbonated drinks also contained high values, between 0.30 and 0.70 mg/l. These findings showed a probable cause-andeffect relationship between high arsenic content in water supply and dermatologic lesions noted in a high percentage of Antofagasta's inhabitants. A water treatment plant, that started to operate in 1970, was built to solve the problem.
The present report aims to evaluate the actual state of the arsenicism problem in the city of Antofagasta 6 yr after the plant began operation. It was carried out by a clinical and epidemiological approach and with the determinations of arsenic content in hair and nail clippings of the general population and in school children 6 years of age or less. These children were probably not exposed to the intoxication risk.

Materials
Arsenic determinations in hair and nail clippings samples were carried out on 411 subjects, 200 of whom were 6 years of age or less and perhaps not exposed to arsenicism since birth, and 200 subjects over 6 years that were born and lived continously in Antofagasta.
The sample for studies of cutaneous lesions comprised 645 school children; 306 under 6 years and 339 over that age (Table 3).

Method
Arsenic content was determined in carbonated beverages, cultivated vegetables, and biologic products (hair and nails) by using the diethyldithiocarbamate method.
Clinic examination (by a physician) of a representative sample of school children population was carried out to establish the presence or absence of cutaneous lesions attributed to arsenicism.

Results
The results are summarized in Tables 4-10. Table 4 shows that cutaneous lesions are not found in school children younger than 6 years.  (Antofagasta, Chile, 1968-1970and 1976 Table 8 shows the range of variation of As values in nail clipping samples. Only 13.3% of the cultivated vegetables samples show arsenic contents above normal values (Table 9). Mean values of arsenic content in soft drinks dropped from 0.24 mg/l. in 1968 to 0.06 mg/l. in 1976 (Table 10).

Discussion
In this preliminary study, 6 years after the water treatment plant began operation, the problem had disminished considerably relative to the previous report (1971).
The absence of cutaneous lesions in school children under 6 years suggest two hypotheses: they may have not been produced because of the short period of exposure to arsenic in the drinking water, or that the arsenic content is under the necessary level to produce clinical manifestations.
The fact that the arsenic contamination problem continues, although very diminished, suggests that continued surveillance and continued investigations are desirable to follow up the clinical and epidemiological manifestations of this problem. These manifestations can be cutaneous lesions produced by a cummulative effect of the arsenic ingested, or other systemic clinical manifestations attributed to arsenic consumption and perhaps produced earlier than the cutaneous sign.
Sanitary engineering studies will be necessary to improve the system of water purification, in order further to lower the arsenic content.
With periodic evaluation of the chronic arsenic intoxication problem we will have an integral and complete view of the illness. August 1977 105