Monitoring of the exposure to platinum-group elements for two Italian population groups through urine analysis

Abstract

It is well recognized that automobile catalytic converters are the main source of Pd, Pt and Rh (also called platinum-group elements (PGEs)) in an urban atmosphere. Over recent years, urinary biomonitoring of PGEs has gained considerable importance in assessing the individual human exposure to these elements. This paper reports the concentration ranges of PGEs in the urine of 257 Italian subjects, aged between 23 and 88 years. Subjects were selected on the basis of standardized criteria in two different Italian cities, so as to represent a small urban area surrounded by an essentially rural environment and characterized by low automobile-traffic density (Foligno) and a large urban area with almost constant high-traffic conditions (Rome). The determination of PGEs was performed by sector field inductively coupled plasma-mass spectrometry (SF-ICP-MS) after 1:4 (v/v) dilution of the samples. The 5th and 95th percentiles for PGEs in urine of subjects living in Foligno were the following (in ng l⁻¹): Pd 1.99–17.2, Pt 0.24–3.08 and Rh 0.53–14.8. The 5th and 95th percentiles in the urine of subjects from the area of Rome were (in ng l⁻¹): Pd 0.71–17.0, Pt 0.49–8.13 and Rh 4.10–38.6. Platinum and Rh median concentration values showed large and significant differences (P<0.0001) between the two urban settings considered (0.52 and 3.50 ng l⁻¹ for Pt and Rh in Foligno, respectively, and 1.70 and 12.85 ng l⁻¹ for Pt and Rh in Rome, respectively). On the other hand, no striking differences were found in the Pd concentration (median value of 6.02 ng l⁻¹ in Foligno versus 7.79 ng l⁻¹ in Rome). The sex variable correlates only with Pd concentration (P=0.05), pointing out that in males concentrations are higher than in females.

Introduction

With the adoption of Pd-, Pt- and Rh-containing catalytic converters in automobiles, the widespread environmental contamination by these metals has dramatically increased [1], [2], [3], [4]. Recent investigations have shown that these elements have already accumulated in roadside and airborne dust, soil and grass, thus raising concern about the possible noxious effects on humans [5], [6], [7], [8], [9].

Because of their chemical inertness, noble metals and their compounds have for a long time been considered as harmless. On the other hand, over the past decade more information has been gained about the effects of platinum-group elements (PGEs) in humans, even if mostly related to occupational exposures, i.e. in the refinery and automobile industry, in the field of iatrogenic exposures in dentistry (Pd) and in cancer therapy (Pt). In particular, Pt salts are a cause of allergic reactions in workers of platinum refineries [10], [11]. Cisplatin and carboplatin, used as antineoplastic agents in the medical treatment of several tumours, are well-known cytotoxic compounds and increases in mutagenic events have been observed for health care personnel manipulating such drugs [12]. The toxicological data on Pd and Rh are meagre and sometimes conflicting. One case report of occupational asthma caused by Pd has been published [13], while potential risks of allergic reactions when Pd is used in dental casting alloys have been reported [14]. Finally, cytotoxic effects of Pd and Rh salts have been ascertained, although by far lower than that of some Pt complexes [15].

There is experimental evidence that after ingestion and inhalation of Pt compounds the metal can be found in various body organs [16]. For example, some studies report on the long-term urinary excretion of Pt in cancer-affected patients treated with cisplatin and on the presence of elevated Pt concentrations in their liver [17], [18].

In this context, biological monitoring plays a pivotal role in assessing the individual human exposure to PGEs and the health risks associated with this exposure. Through proper planning and conduct of biological monitoring schemes and full implementation of analytical quality control and assurance systems, sets of specific concentration ranges for PGEs can be arrived at, which can be used to detect differences between occupational and environmental exposure to PGEs. As urine is the major excretion route for many noxious substances entering the organism, it can be considered as one of the most useful materials for biomonitoring activities, also due to ease of sampling. Urinary excretion of PGEs has been already used as a marker of the load of these metals in the urban environment in consequence of their release from automotive catalytic converters [19], [20], [21], [22], [23], [24], [25], [26]. Table 1 reports the available literature data on PGE concentrations in urine of control population groups as well as of individuals exposed to heavy-traffic conditions. Data of this kind are sparse, mostly due to the analytical difficulties in measuring the very low concentrations expected for these elements in the said matrix. In general, the Pt concentration in urine is in the order of 10 ng l⁻¹, while the Pd level is reported to be about one order of magnitude higher. As regards the Rh urine content, the only data available (mean concentration of 10.5 ng l⁻¹) refer to environmental exposure of children. For individuals heavily exposed to traffic, a slight increase in Pd concentration can be noted (but not in Pt content) when compared with control persons (Pd mean values of 52.2 ng l⁻¹ in urine of road workers versus 31.0 ng l⁻¹ for the control group) [24]. On the other hand, Schierl found a median concentration of Pt in control subjects similar to that in exposed subjects, such as bus drivers (3.6 ng l⁻¹ versus 2.8 ng l⁻¹) [22]. It should be considered, however, that these studies dealt with a limited number of subjects. An investigation performed on a greater number of subjects (310 children from urban and sub-urban areas of Rome) revealed significant differences in the levels of Pd and Rh (but not of Pt) as a function of traffic density [25].

Due to the paucity of such data and in order to better understand the contribution of car exhausts to the body load of PGEs, a biomonitoring campaign was launched in the framework of the EU project “Assessment of environmental contamination risk by platinum, rhodium and palladium from automobile catalysts” (CEPLACA) in the years 1998–2000 to shed further light on this issue. A group of 257 Italian subjects, aged between 23 and 88 years, was set up in order to evaluate the influence of traffic density on the urinary PGEs levels by comparing subjects living in a small urban area surrounded by an essentially rural environment (Foligno, ca. 55,000 inhabitants) with those living in an urban setting (Rome, ca. 3,500,000 inhabitants).