The Trend of Trace Elements (Cd, Ni, Pb) from PM2.5 and PM10 Aerosols and its Effect on Human Health in Bucharest, Romania

The comprehensive investigation of the elemental characteristics in fine and coarse particles at Bucharest was carried out. The daily samples of PM2.5 and PM10 particulate matter were collected at eight monitoring stations for a one-year period, and concentrations of Cd, Ni, Pb elements were analyzed. The results show that PMs and trace elements were present in high concentrations in Bucharest. The annual concentrations of PM10 and PM2.5 were 31.57 μg/m 3 and 21.30 μg/m, respectively. In Bucharest, the average concentration ratio of fine (PM2.5) and coarse particulates (PM10) was 0.67. Trace elements concentration carried by the PM2.5 was higher than the concentration detected from PM10. The Cd, Ni, and Pb accumulation was higher by 55.16%, 37.46% and 29.14% in fine particles than in coarse particles. The annual mean trace element concentration from PM2.5 and PM10 was in the case of Cd 0.22/0.24 ng/m , for Ni 3.28/3.14 ng/m and for Pb 5.61/6.44 ng/m, respectively. The highest Spearman correlation was found between Cd and Ni with correlation coefficient of 0.62 in PM2.5 and 0.48 in PM10, which suggests that they share common sources. The health risk indexes were estimated for both adults and children thanks to the trace elements from the particulate matter (PM), and the results revealed that inhalation was the major exposure pathway in both cases.


1.Introduction
Particles (PM) with an aerodynamic diameter less than 10 μm lead to many premature deaths worldwide and contribute to an increase in cardiovascular disease [1,2]. In addition fine particles (PM2.5, particles ≤ 2.5 μm in aerodynamic diameter) carries greater danger to human health than the coarse particles (PM10) [3]. Trace elements (TEs) generally represent a small fraction of atmospheric particles (PM), but they nevertheless have a significant impact on the environment and human health [4,5]. Toxic trace elements such as As, Ni, Cd, Pb are considered as carcinogens with potential health risks [6]. There are three possible routes of exposure to toxic elements: ingestion, inhalation, and skin absorption, and have an accumulation potential in the biological systems, especially in the fatty tissues [7]. Therefore, the elemental characterization of PM particles of different sizes is of great concern. Cd and Ni compounds in particulate matter, mainly originate from coal and fuel oil combustion processes, metallurgical industry, and road transport, respectively [8]. A number of statistical techniques, including correlation matrix, and health effects calculation were utilized to identify the influences of diverse emission activities. The results provide useful insights for developing effective emission reduction strategies. The trace elements composition in PM10 has been studied by a number of studies worldwide, in Romania by [9][10][11][12][13][14][15] in Europe by [4,[16][17][18] and in other continents by [7,[19][20][21][22]].

Materials and methods
Daily trace element concentrations (Cd, Ni, Pb) were determined in PM2.5 and PM10, which were sampled in Bucharest, the capital of Romanian, between January 2018 and December 2018. Bucharest is the most populated city in Romania has over 2 million inhabitants covering a surface of 228 km 2 with coordinate: latitude 44.4268 °N and longitude: 26.1025 °E. Bucharest has a humid continental climate with an average temperature of 12°C [23]. The main PM2.5 and PM10 pollution in Bucharest comes from intense traffic and industrial activities (CETs) emissions [24]. The daily PM2.5, PM10 and trace elements concentration data were obtained from the National Air Quality Monitoring Network. Regarding the monitoring stations (B1-B8), the trace elements in the case of B1 were determined from PM2.5 and at the remaining stations the data were obtained from PM10fraction.
The temporal variation of daily concentrations of PM2,5 and PM10 were statistically analyzed, hence the most important correlations were identified. Spearman correlation coefficient (Ri386 3.5.3.) was used to determine the correlation between PM and trace elements (Cd, Ni, Pb) concentrations.
To determine the exposure levels of trace elements via inhalation, ingestion and dermal absorption the health risk model developed by the US Environmental Protection Agency (EPA) was used [25]. The quantitative assessment of the cancer risk (CR) was carried out for adults and children. Risk characterization was quantified separately for carcinogenic and non-carcinogenic effects. The non-carcinogenic risk was assessed by the hazard quotient (HQ). HQ and carcinogenic risks (CR) posed by heavy metals in PM10 via ingestion, inhalation and dermal contact were calculated. Values below 1E-06 for individual chemicals and pathways show negligible cancer risks.

3.Results and discussions
The ambient atmospheric concentrations of PM2.5, PM10 and trace elements at the Bucharest region are summarized in Table 2. Using descriptive statistics the mean, minimum, median, maximum, 25 th -and 75 th percentile values, and confidence intervals were calculated. During the studied period, the average concentration of PM10 in Bucharest was 31.57±1.33 µg/m 3 which is 57.85% higher than the WHO's acceptable limit (20 µg/m 3 WHO, 2005). In the case of PM2.5, the annual concentration was also 113% higher than the admissible level (10 µg/m 3 ). Overall, the Pb and Ni contributions were the highest.
According to the WHO guidelines the maximum annual average safe level of heavy metals is 0.5 μg/m 3 for Pb, 5 ng/m 3 for Cd, and 20 ng/m 3 for Ni, respectively.
In Bucharest, the average concentration ratio of PM2.5 and PM10 was 0.67, meaning that for the same concentrations of PM10 and PM2.5, trace element enrichment was significantly higher in PM2.5 than in PM10. The Ni, Cd and Pb accumulation in fine particles was higher than in coarse particles by 55.16%, 37.46%, and 29.14%, respectively.

Temporal variations
The temporal variations of trace element concentrations in PM2.5 and PM10 at Bucharest are presented separately ( Figure 1). Overall, the trace elements presented similar temporal patterns in both sizes. On the other hand, time series analyzes revealed drastic concentration variations for Cd, Ni, and Pb, mainly higher during warm period and significantly lower in the cold period (December-February) which is strongly correlate with the traffic intensity (higher in summer). In early spring thanks to the stronger wind speed and lower vegetation favored the suspension of soil/road dust. In the case of particulate matter, annual evolution shows the highest peak concentrations in winter and a minimum level in summer, thanks to the meteorological variables [26][27][28][29].

Spearman correlation
Spearman correlation analysis was used to investigate the correlation between all the trace elements from PM2.5 and PM10 (Figure 3). The monthly average concentrations were used for the correlation analysis and Pvalues of 0.05 (5%) were considered statistically significant. Trace elements originated from the fine particulars show a higher correlation level than those from the coarse particulate. The Spearman correlation between monthly means of PM's and trace element concentration in 2018 has been studied separately for the B1 monitoring station (PM2.5) and the B2-8 (PM10) respectively. In the B1 monitoring station, a higher correlation was found between the Cd and Ni (r=0.62). A moderate positive correlation was detected between the Pb and Ni (r=0.45). A moderate negative correlation was identified between Ni and PM2.5 (r=-0.42) and between Pb and PM2.5 (r=-0.45) as well, which suggests that the source origin of trace elements differs from PM2.5 sources.  Furthermore, at B2-8 monitoring stations, the correlation level between the trace elements and PM10 concentration was less significant than in PM2.5. Between the Cd and Ni, the correlation coefficient was 0.48 which suggests common sources. In contrast to PM2.5, positive moderate correlation was found between the PM10, Ni (r=0.36) and Cd (r= 0.31).

Health risk assessment by toxic metals in PM 2.5 and PM10 Non-carcinogenic risk assessment
Inhalation is the primary route of direct exposure to particulate bound trace elements. The HQ values for the three exposure pathways are presented in Table 3. The HQ values for dermal and ingestion exposure for both groups, adults, and children, in Bucharest regions, were lower than the safe limit (=1). In the case of ingestion and dermal absorption, significant differences were observed between children and adults thanks to their behavior and physiological activities [30]. The HQ value for Pb could not be calculated for the reason that US EPA does not establish the threshold value (RfCi) for different exposure routes. Via inhalation, the HQ value for Ni in PM2.5 was higher than the safe limit (=1) in both cases, adults (2.70E+00) and children (2.70E+00). Regarding the HQ value from PM10 similar tendency was obtained (2.65E+00), indicating that Ni might pose a non-carcinogenic risk to adults and children. The HI (sum of all the elements under consideration) value increased to 6.12E+00, indicating the accumulative non-carcinogenic health risk due to inhalation exposure of the mixture of elements.

Cancer risk assessment
For the investigation of carcinogen risks in PM2.5 and PM10 three trace elements (Cd, Ni, Pb) were taken into consideration, because these are classified as carcinogen/probably carcinogenic/possibly carcinogenic to human health according to IARC (International Agency for Research on Cancer).
The carcinogen risk via inhalation for adults, in all examined trace elements, was lower than the acceptable limit (1E-06). Adults had a higher probability of experiencing carcinogenic risk compared to children. The HI value increased to 1.52E-05 indicating the accumulative cancer risk due to inhalation exposure of the mixture of elements (Table 4.).
In order to figure out the concentrations level, the values obtained in Bucharest from the PM2.5 and PM10 were compared with those measured from different parts of the world (Table 5.).  Comparatively, it can be said that the Cd concentration (0.22/0.24 ng/m 3 ) is much higher than in the USA, Spain, and Taiwan, respectively. The Ni concentration (3.28/3.14 ng/m 3 ) is higher than in Spain. The Pb concentration in the Bucharest region (5.61/5.44 ng/m 3 ) is between the USA and Spain (lower in the USA and higher in Spain).

4.Conclusions
The time-series analysis results show that the annual mean concentration of PM2.5 and PM10 was 21.30 µg/m 3 and 31.57 µg/m 3 , respectively. These concentrations exceeded the annual mean standard established by the European Union (PM2.5-10 µg/m 3 and PM10-20 µg/m 3 ). Although the PM10 concentration has decreased since the implementation of the European environmental legislation, the daily limit values exceeded the maximum permissible levels almost continuously; therefore Bucharest is under the infringement procedure regarding the air quality. Briefly, all trace elements in fine particles (PM2.5) were higher enriched than in coarse particles (PM10). The mean metal concentration decreased in the following order: Pb>Ni>Cd. The seasonal variation in PM concentration was distinguishable; the highest concentration was observed during the winter season, followed by autumn, spring, and summer, respectively. Regarding the trace element distribution over the years, the maximum peak was found in the warm season and minimum in the cold season, thanks to the traffic intensity. Health hazard assessment identified inhalation as the leading pathway of particle-bound trace element exposure to humans. The multi-elemental hazard index (HI) indicated greater health risks in case of mixture of elements.