Historically, lead (Pb) has been one of the most widely used metals due to its useful properties such as low melting point, high density and ductility. Decades of widespread industrial and commercial use of leaded products, most notably petrol and paint, have left a legacy of environmental contamination which may contribute to chronic Pb exposure and acute Pb toxicity [1,2,3,4].

Chronic Pb poisoning appears progressively and is not specific [5]. Chronic exposure may trigger an acute presentation. The specific indications of acute lead toxicity involve abdominal pain (Pb colic), constipation, irascibility, neuropathy, muscle inflammation, joint pain, headache, anorexia, reduced sexual desire, concentration and short-term memory problems, nausea, lead lines on gums, anaemia, basophilic stippling of red blood cells, and kidney diseases [6,7,8]. Many outcomes of lead toxicity are related to its interactions with crucial components like calcium, enzymes and other proteins [9]. Lead poisoning can result from ingesting or inhaling lead compounds [10]. It can also occur as a result of dermal contact with organic lead, though to a lesser extent, or bone reabsorption of leaded bullets. Around 90–95% of absorbed lead is reserved in the cortical bone and teeth, liver, brain and kidneys. 75% of excreted lead is removed by the kidneys; the remainder is eliminated via the gastrointestinal tract, sweat, and skin or is accumulated in the nails and hair [7, 11, 12].

In adults, the greatest absorption of Pb occurs via the respiratory tract, where up to 95% can be absorbed in the lungs. When Pb is ingested approximately 5–20% is absorbed, largely in the duodenum.

Diagnosis of Pb poisoning is based on elevated Pb levels in the blood, specifically a BLL of ≥10 μg/dL. Discontinuation of contact with the lead source is a vital step in treatment. Most outcomes of lead poisoning can be reversed if lead toxicity is diagnosed swiftly and the source eliminated. Chelation therapy may be necessary in acute Pb poisoning in order to more rapidly reduce the BLL and facilitate recovery [6, 13].

Pb poisoning outbreaks around the world have typically occurred as a result of significant environmental contamination from activities such as Pb mining or smelting. Examples include the Pb poisoning outbreak in Zamfara State, northern Nigeria, in which several villages were affected by significant environmental Pb pollution due to mining activities. Examples of unusual Pb incidents are also available in the literature and include acute Pb poisoning occurring from the use of topical Ayurvedic treatment [14, 15] and culinary spices [16, 17].

There are several accounts of Pb toxicity arising from drug use, most involving opium [11, 20], though reports of cases involving marijuana [18] or methamphetamine [19] are also available. The earliest account of lead contaminated opium was in 1973 and was as a result of cross contamination from the kitchen equipment used to prepare opium for consumption [20].

The process of mass opium manufacture typically involves reducing opium poppies to brown sticky paste and sun drying, during which impurities such as Pb may be introduced or concentrated [21,22,23]. Refined opium, locally referred to as Shireh, is a strong opium produced by refining raw opium, known locally as Taryak, in boiling water, heating and filtering to remove insoluble materials [24].

Several sources of Pb contamination have been postulated in the literature: the adulteration of opium with Pb to increase weight, either at the point of production or at a local level [7, 25]; contamination from the processing equipment used during the production of the opium [20, 26]; and/or contamination of land on which opium is grown [27, 37]. It is suggested that other compounds like lead oxide, lead nitrate, lead acetate as well as Indian hair colours which contain lead can also be added to opium [27].

Some Iranian researches have analytically confirmed the presence of Pb in opium [6, 25]. Several others have reported lead toxicity in opium users [5, 26, 28, 29].

Iran shares a border with Afghanistan, a major producer of opium, and exportation of opium across this border has been identified as one of the main routes for transit of opium worldwide [30, 31]. Consequently, opium availability and use is a major issue in Iran, which may create a platform for opium adulteration and an increased risk of acute Pb exposure [30, 31].

It has been shown that Pb readily accumulates in the capsule of poppy plants grown in Pb contaminated soil [32]. Afghanistan, provides about 90% of the world’s opium [33]; the United Nations Office on Drugs and Crime reports that that average yield of opium has increased in certain parts of central and southern Afghanistan [34]. Afghanistan’s Pb mineral rich deposits and Pb mines are also largely distributed in these regions [35] so it follows that an increase in opium production grown on Pb contaminated land could potentially increase the Pb concentration in opium, this warrants further investigation.

It is feasible that multiple sources are responsible for the lead content in opium, herein lies a gap in the current knowledge. What is clear from published case reports and this current study, is that the number of opium users being admitted to hospitals for Pb poisoning appears to be increasing in Kerman and other parts of Iran [29, 36].

Meybodi determined that the prevalence of opium user patients with Pb poisoning in Tehran, Iran’s capital city, over a one-year period (2006 and December 2007) was limited to 25 patients [28]. In 2009 a study in Kerman showed no significant difference in the BLL of opium users (n = 50) and the control group (n = 43) [37].

Although in recent years there has been an increase in cases of lead poisoning due to opium use in some cities of Iran such as Birjand and Ardabil [8, 23], Pb poisoning related to opium use had until recently remained relatively rare and to our knowledge such poisoning was generally only reported as isolated cases.

The study herein highlights an acute increase in cases of lead poisoning of opium users reported over a short time period in Kerman Province, Iran. The aetiology of this increase is unknown. Given the severe outcomes of significantly increased serum level of Pb, this study also examines the clinical effects of acute Pb poisoning in opium users.