Measurement of lead, cadmium, arsenic, nickel and mercury by INAA and PIXE
M.C. Freitas, M.A. Reis, M.M. Farinha, S.M.
Almeida, C.C. Costa
ITN
– Instituto Tecnológico e Nuclear, 2686-953 Sacavém, Portugal, e-mail:
CFREITAS@ITN1.ITN.PT
ABSTRACT
The European Council Directive 96/62/CE from 27th September 1996 concerning air quality evaluation in the European Union is being applied by steps. The Directive 1999/30/CE from 22nd April 1999 implants regulation for PM10, lead and preview the PM2.5 control for a near future. Our institute is involved in the determination of chemical elements in airborne particulate matter since 1993. Nuclear analytical techniques INAA and PIXE are used for that. This work shows the possibility of using these two techniques to analyse chemical elements submitted to regulation and presents data on these elements for a few places in Portugal.
INTRODUCTION
The awareness of environment degradation in a way that may influence health has increasingly been attested by several epidemiological and toxicological studies in many places of the globe. Recent studies show that suspended heavy metals in the atmosphere are dangerous for health (Christensen et al., 1994). Heavy metals are present in the atmosphere mainly in form of suspended particles. Two classes are presently used to describe airborne particles: PM10 and PM2.5. This reports to particle size and comprises particles having less than 10 mm of aerodynamic diameter (PM10), or particles having less than 2.5 mm of aerodynamic diameter (PM2.5). The association of airborne particles to mortality is evident in PM2.5 (Cohen, 1998).
The European Council Directive 96/62/CE from 27th September 1996 establishes a stepwise process for adoption of limit values for PM10, Lead, Cadmium, Arsenic, Nickel and Mercury in order to protect the human health especially in the more vulnerable population. The European Council Directive 1999/30/CE from 22nd April 1999 defines the limit values for PM10 and lead and introduces the need for PM2.5 sampling into EU regulation. The PM10 limit value for human health protection is settled in 50 mg/m3 for 24 hours average and 40 mg/m3 for year average. The human health protection annual average limit value for lead is settled in 0.5 mg/m3.
The reference method establishes gravimetry for PM10 measurement and atomic absorption spectroscopy (AAS) for lead determinations. At ITN PM10 and PM2.5 gravimetric measurements as well as multielement characterisation of airborne particles has been made systematically since 1993. Alves et al. (1998a) presents the first set of multielement airborne particle characterization results using PIXE, INAA and gravimetric measurements and reports a campaign held in Lisbon from October 1993 to January 1995. PIXE and INAA measurements obtained at ITN have been compared to AAS data in several intercomparison runs.
In this work data for PM10, PM2.5, lead, cadmium, arsenic, nickel and mercury is presented for five measuring stations. Three are located up to 10km North from Lisbon (Bobadela, S. João da Talha and Quinta da Piedade) and two are placed in the Setúbal peninsula, about 50 km south from Lisbon (Palmela and Faralhão).
The North of Lisbon is a very industrialised area and at same time is very populated which makes more dangerous the degradation of the air quality. Last year a new domestic urban waste incinerator was started in this area. This work is associated with the monitoring studies of this structure and it is being made under contract. The sampler situated in Bobadela has been working since 25th January 1999, the S. João da Talha (SJT) and Quinta da Piedade (Piedade) started working seasonally in 7th March 1999.
The sampling stations located in the region of Setúbal have been used for several projects sponsored by Electricity of Portugal, Portuguese Environmental Ministry and the International Atomic Energy Agency, aiming to study the inorganic atmospheric pollutants dispersion in this area. In Palmela and Faralhão the stations are working since June 1994 and January 1995, respectively.
METHODOLOGY
Air collection is made with Gent samplers. This kind of sampler is equipped with a SFU (stacked filter unit) which carries two 47 mm diameter NucleporeÒ polycarbonate filters. Filters of 8 and 0.4 mm pore sizes are used in the first and second stages respectively. Air is sampled at a rate of 15 l/min, which allows the collection of PM2.5 in the second stage. The samplers inlet is a PM10 separator so that the first filter collects only coarse particles (PM10-2.5) having aerodynamic diameter between 2.5 and 10 mm. The samplers in the North from Lisbon area work during 24 hours periods, 40 minutes out of each hour totalling 16 hours per day. Sampling is made twice a week: one on Sunday day and one on midweek. In Palmela and Faralhão the samplers work 10 minutes out of each 2 hours, corresponding to 14 hours of sampling per week. The filters are replaced weekly. A comparison of the two procedures was reported by Alves et al (1998b).
Filter loads are measured by gravimetry using a balance with 10 mg sensitivity and elemental analyses are carried out using INAA (Freitas, 1989) and PIXE (Reis, 1992) techniques. For elemental analysis the filters are cut into three parts: one half is analysed by INAA, one quarter is analysed by PIXE and the other quarter is kept for other possible measurements of replicates.
Recently some improvements were made in INAA procedures, which allow a lower detection limit, especially for cadmium. These will be published elsewhere (Freitas et al., 2000).
|
Fig1: Ratio for Ni, As, Cd, Hg and Pb to Lichen (L1), Lichen (L2) and air filter AIR-3/1 (Air) |
QUALITY CONTROL
Fig. 1 presents the ratio between the values obtained by our Institute and reference values from NAT-5 intercomparison run and AIR-3/1 certified reference material from IAEA.
For lichen sample L1 good results were obtained for As, Hg and Pb. Ni result for L1 was not considered since a certified value was not available. For lichen sample L2 the results for Ni and Hg are close to the certified ones. Pb the ratio for L2 is high, nevertheless a totally compatible value was determined by our Institute in IAEA-336 intercomparison run which is actually the same material, showing consistence in our results.
For Air 3/1 sample only As and Cd were evaluated. The values obtained are consistent with the reference ones
RESULTS AND DISCUSSION
|
Fig2. Relation between the ratio Zn/Pb and Pb for PM10 in Bobadela. |
Lead
In Table 1 statistics are shown for Arsenic, Cadmium, Mercury, Nickel and Lead for PM2.5, PM10-2.5 and PM10 fractions and for the five stations.
TABLE 1: Statistics for Pb, Cd, Ni, As and Hg. (Values in ng/m3)
|
|
|
Pb |
|
|
Cd |
|
|
As |
|
|
Ni |
|
|
Hg |
|
|
|
|
|
<x> |
StD |
Max. |
<x> |
StD |
Max. |
<x> |
StD |
Max. |
<x> |
StD |
Max. |
<x> |
StD |
Max. |
|
PM2.5 |
BOB |
28.9 |
54.5 |
379 |
2.54 |
2.88 |
8.8 |
0.88 |
2.95 |
26.6 |
4.07 |
3.27 |
17.3 |
0.177 |
0.188 |
1.07 |
|
|
SJT |
22.6 |
19.0 |
94 |
1.59 |
1.72 |
6.2 |
0.67 |
0.387 |
1.83 |
8.4 |
8.0 |
42.9 |
0.211 |
0.173 |
0.64 |
|
|
PIE |
12.5 |
7.4 |
35.8 |
1.16 |
0.59 |
1.71 |
0.225 |
0.112 |
0.422 |
2.53 |
1.31 |
5.7 |
0.116 |
0.083 |
0.421 |
|
|
FAR |
18.9 |
8.2 |
40.6 |
n.a. |
n.a. |
n.a. |
0.62 |
0.409 |
1.88 |
3.32 |
1.16 |
6.7 |
0.220 |
0.231 |
1.30 |
|
|
PAL |
21.2 |
9.9 |
60 |
n.a. |
n.a. |
n.a. |
0.436 |
0.232 |
1.15 |
3.14 |
1.15 |
7.0 |
0.218 |
0.235 |
1.11 |
|
PM10-2.5 |
BOB |
29.7 |
55 |
290 |
1.01 |
- |
1.01 |
0.62 |
2.92 |
22.4 |
3.09 |
2.21 |
10.1 |
0.428 |
1.69 |
12.7 |
|
|
SJT |
30.0 |
42.3 |
202 |
1.21 |
0.268 |
1.36 |
0.79 |
1.73 |
8.5 |
5.6 |
5.5 |
31.3 |
0.274 |
0.201 |
0.70 |
|
|
PIE |
9.8 |
8.4 |
44.7 |
- |
- |
- |
0.186 |
0.102 |
0.432 |
1.88 |
1.39 |
6.1 |
0.080 |
0.0484 |
0.208 |
|
|
FAR |
8.6 |
5.3 |
30.6 |
n.a. |
n.a. |
n.a. |
0.387 |
0.282 |
1.61 |
1.73 |
0.78 |
3.52 |
0.263 |
0.235 |
0.96 |
|
|
PAL |
12.1 |
7.8 |
48.7 |
n.a. |
n.a. |
n.a. |
0.251 |
0.193 |
0.88 |
2.54 |
1.19 |
7.0 |
0.189 |
0.142 |
0.66 |
|
PM10 |
BOB |
49.2 |
98 |
621 |
2.69 |
3.25 |
9.8 |
1.21 |
3.65 |
26.7 |
6.4 |
5.2 |
22.0 |
0.442 |
1.47 |
13.3 |
|
|
SJT |
48.0 |
48.1 |
202 |
1.73 |
1.63 |
6.2 |
1.34 |
1.60 |
8.5 |
13.3 |
11.6 |
54 |
0.382 |
0.345 |
0.97 |
|
|
PIE |
19.1 |
14.2 |
73 |
1.16 |
0.59 |
1.71 |
0.361 |
0.190 |
0.70 |
3.77 |
2.62 |
11.2 |
0.167 |
0.107 |
0.494 |
|
|
FAR |
24.0 |
10.7 |
51 |
n.a. |
n.a. |
n.a. |
0.85 |
0.54 |
2.48 |
3.04 |
2.03 |
8.3 |
0.390 |
0.433 |
2.27 |
|
|
PAL |
31.2 |
15.0 |
96 |
n.a. |
n.a. |
n.a. |
0.60 |
0.292 |
1.37 |
4.82 |
2.74 |
14.1 |
0.361 |
0.328 |
1.23 |
n.a. – not analysed
Cadmium
In cities Cd ranged from 0.006 to 0.36 mg/m3 in the USA, from 0.002 to 0.05 mg/m3 in Europe and from 0.01-0.053 mg/m3 in Japan. In remote areas these values are a factor of 10-1000 lower, whereas in polluted areas much higher values may be found (Seiler et al., 1994). This element was not detected in Palmela and Faralhão. In the North from Lisbon stations Cd was detected very seldom but mainly in S.J.T. and in PM2.5 fraction. In the values presented in Table 1 it can be seen that whenever Cd was determined, values around and below the typical minima for EU cities were found.
Arsenic
The air in industrial zones contains 0.3-120 ng/m3. Average contents in Germany are 5-20 ng/m3 and at the South Pole 0.007ng/m3 (Seiler et al., 1994). In Piedade As was found in lower concentrations. The other stations have similar concentrations in PM2.5. In PM10 the concentrations are higher in Bobadela and S.J.T. All values are, nevertheless near the typical minima for industrial areas.
Nickel
Nickel concentrations at remote locations were about 1 ng/m3. Ambient levels for nickel in air ranged from 5 to 35 ng/m3 at rural and urban sites. In industrialised regions and large cities, atmospheric nickel concentrations as high as 120-170 ng/m3 have been recorded (Seiler et al., 1994). SJT has higher concentrations in PM2.5 and PM10.
Mercury
In PM2.5 fraction Hg concentrations in the five stations are similar. In PM10 fraction Piedade has lower concentrations.
CONCLUSIONS
For the elements for which regulation exists or is near to be implemented, the levels measured show an air quality comparable to the best in European cities.
It was shown that INAA and PIXE can be used for standard monitoring of airborne trace element concentrations. The possibility for simultaneous assessing other elements without additional costs enforces the possibilities of use of these techniques. The prompt identification of two lead sources and the one responsible for the highest concentrations measured, based on the Zn to Pb ratios is an example of the potentiality of the use of these techniques in standard monitoring conditions.
REFERENCES
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