Comparison of moss bag and native moss technique in monitoring airborne particulate and toxic elements

Nguyen Thi Minh Sang; Le Hong Khiem; Son An Nguyen

doi:10.32508/stdj.v24i2.2531

Section: ENGINEERING AND TECHNOLOGY

Comparison of moss bag and native moss technique in monitoring airborne particulate and toxic elements

Nguyen Thi Minh Sang ¹

Le Hong Khiem ²

Son An Nguyen ^{1, *}

Dalat University, Dalat, Vietnam
2Institute of Physics of Vietnamese Academy of Science and Technology, Hanoi, Vietnam

Correspondence to: Son An Nguyen, Dalat University, Dalat, Vietnam. Email: sonna@dlu.edu.vn.

Volume & Issue: Vol. 24 No. 2 (2021) | Page No.: 1967-1974 | DOI: 10.32508/stdj.v24i2.2531

Published: 2021-05-15

Abstract

Introduction: In Vietnam, the government has invested in monitoring stations in a few big cities like Hanoi and Ho Chi Minh City, which have transportation centers and industrial zones, to assess and predict levels of air pollution. However, the main disadvantage of installing monitoring stations is the cost of investment for operations, maintenance, and equipment. It is also time-consuming to collect and analyze the results. Therefore, it is generally not suitable for the country as a whole.

Methods: Using mosses to monitor air quality brings qualitative and quantitative data with simple, environmentally-friendly economic methods. Mosses have particular biological characteristics that make them very suitable adsorbents for a wide variety of chemical elements. When used as transplants like moss bags, allow them to monitor a highly dense sampling network of any site easily. Mosses are bioindicators, plants with artificial roots.

Results: In this study, moss bag and native moss were the two methods used to evaluate the accumulation of trace elements in air through Barbula Indica. Observations showed that both methods could detect the same elements: Al, Si, P, S, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Rb, Y, Sb, Ba, Pb, and U. However, the accumulation of the elements in native moss is higher than in moss bag. The main reason is that the absorption efficiency of native moss in air-deposited elements is higher than in moss bags.

Conclusion: Moss bags have been used most extensively and successfully in urban areas, where vegetation samples are either unobtainable or are poorly located to the source. These areas can lack moss, or the native moss simply does not grow during the dry season.

Keywords: Air pollution, native moss, moss bag, air monitoring, Babular Indicar

INTRODUCTION

Biomonitor represents a good solution for air quality monitoring. Vuković, 1 has shown that bioindicator monitoring is a simple and cost-effective method to evaluate pollutants in the atmosphere. Biomonitor organisms like lichens and moss can be considered bioindicators or bio accumulators.

The moss bag technique was introduced by Goodman and Roberts2. Since then, it has been a valuable technique for detecting airborne contaminants, such as heavy metals and nonmetals.

The moss bag technique is helpful in doing a detailed survey of polluted urban areas, where moss cannot grow naturally3. Moreover, this technique does not require maintenance or a source of electricity to continue operation. Another essential difference between the moss bag technique and instrumental measurements is sampling time4. Instrumental measurements are usually done in a short period, providing daily pollutant concentrations. On the other hand, Moss bags play a long-term role in the collection of statistical pollutants. Long-term sampling is a prerequisite for assessing the cumulative exposure to a given contaminant and its harmful effect on human health.

Since 2014, Vietnam has participated in projects with European countries to investigate environmental pollution through metal deposition in the air. Together, they have developed research directions on air pollution on the moss indicator. Initially, works related to air pollution by the technique were published5, 6, 7, 8.

In this study, two methods are used: native and moss bag. The method of detection is Total Reflection X-ray Fluorescence (TXRF), a multi-element analysis technique. It is used to determine qualitative and quantitative elements from the air in the town of Lac Duong.

Materials — Methods

Sampling area

was used in native moss and moss bag. The time of the survey was from the beginning of November, 2020 to February, 2021. The research was conducted in Lac Duong, Lamdong, Vietnam.

Moss bag exposure was at 2 meters high, the same height as collected fresh moss. Table 1, and Figure 1 show the sampling area.

Table 1

The local moss samples network

No.	Sampling site	Place	Latitude	Longitude
1	LD01	Lac Duong	12.003704	108.412293
2	LD02	Top of Langbiang moutain	12.046528	108.440146
3	LD03	Langbiang tourist area	12.020075	108.419331
4	LD04	Strawbery farm, Lac Duong	12.000362	108.434013
5	LD05	Van Xuan - DT723	12.020963	108.443454

**Figure 1**
**Sampling study area site.**

In this study, 5 sites in Lac Duong were selected to evaluate the effects of different possible pollution sources, specifically:

Native moss preparation

After collection, only the green part of the moss is used for analysis. Therefore, Moss must be handled carefully, avoiding contamination from soil or rock, or other plants. In order to ensure the exact sampling location and minimize the external impact on the collected moss, it is necessary to prepare gloves and zip bags and use GPS to determine the location. Moss sampling points are selected according to pollution sources and clean areas, with a 3 to 5 kilometer distance between the nearest two sampling points.

Moss samples are treated before being put into experimental measurements. The process of treating moss samples (from collection to drying) is shown below in Figure 2.

**Figure 2**
**The process of sample treatment.**

Moss bag preparation

The studies show that the selection of moss spices in the algae bag technique depends on the degree of deformation of the type of algae in the study area and the ability of the algae to absorb and adapt to pollution in that area9. The composition of the chemical elements in old shoots and young buds of moss is different10, and the absorption of the moss bags is also different from that of fresh ones11. In this study, moss was selected as a biological indicator in a moss bag. The steps were as follows:

TXRF technique

This study used a microwave digestion digester MARS 6 (Figure 4) to prepare samples in TXRF technique and homogenize the moss sample. The manipulations were carried out on the MARS 6 microwave digestion machine for moss samples: mix 0.5 g of the dried moss with 10 ml of HNO (Merck) (65%) it in the digestion flask. The digestion time includes 15 minutes for heating to 220 C, 25 minutes for annealing, then natural cooling to room temperature. After finishing the microwave digestion, the moss was completely liquefied.

**Figure 4**
**MARS 6 microwave digestion.**

For analysis on TXRF, the liquefied moss requires an internal standard solution. In this study, the internal standard of Galium was used, with a concentration of 1 ppm.

To create a uniform surface for the sample,10 µl of silicone should be applied to the sample carrier (plate), then dried at 40 C for 20 minutes. The specimen carrier used is a quartz glass disc, which has many advantages: high purity, low background, and easy cleaning12. After the dish is dried, add 10 µl of the sample solution to the measured center of the dish - the diameter of the drop should not exceed 10 mm - and continue to dry at 35C for 40 minutes.

In addition to the size requirement for the diameter, the droplet, after being dripped onto the sample carrier and dried, must also satisfy the thickness requirement - namely, not to exceed 100 µm (Figure 5).

**Figure 5**
**Maximum sample diameter and thickness.**

After the sample preparation, continue to place the carriers' sample on the dryer to allow the sample to dry completely. The measuring system in the TXRF analysis is a S2 PICOFOX device. Steps to create moss samples for the TXRF measurement method can be shown in Figure 6.

**Figure 6**
**Steps to create moss samples for TXRF**.

TXRF Type S2 PICOFOX is a semi-automatic analytical system, qualitative and quantitative analysis of multiple elements, detection threshold to ppb (µg/kg), wide-range analysis of elements from Al to U. Creation of the system includes: X-ray tube (Molipden target), emitted 17.5 keV energy, working at a voltage of 50 kV, current of 1000 µA. The single-function filter is a multilayer crystal made of copper metal. X-ray acquisition detector is a semiconductor detector of SDD type. The system consists of the main components shown in Figure 7.

**Figure 7**
**TXRF S2 PICOFOXTM spectrometer.**

RESULTS

**Figure 8**
**The TXRF spectrum pattern of moss samples.**

Table 2

The concentration of chemical elements in the native moss (mg/kg)

No.	Sample	LD01		LD02		LD03		LD04		LD05		Mean
	Ele.	Con.	± ∆	Con.	± ∆	Con.	± ∆	Con.	± ∆	Con.	± ∆
1	Al	1837	74	1870	75	4031	161	1773	71	1442	58	2191
2	Si	2825	113	4585	183	9970	399	4700	188	3698	148	5156
3	P	287	12	922	37	738	30	520	21	531	21	600
4	S	482	19	1216	49	1286	52	896	36	1090	44	994
5	Ca	781	31	742	30	763	31	770	31	714	29	754
6	Ti	107	4	122	5	194	8	206	8	105	4	147
7	V	6.86	0.37	8.45	0.44	6.69	0.37	10.82	0.53	4.93	0.30	7.55
8	Cr	5.19	0.31	5.37	0.31	10.38	0.52	11.18	0.55	5.10	0.30	7.44
9	Mn	121.00	4.96	61.00	2.53	89.00	3.66	51.00	2.14	53.00	2.21	75.00
10	Fe	3955	158	2400	96	4456	178	2565	103	1928	77	3061
11	Co	1.39	0.16	0.70	0.13	1.24	0.15	0.57	0.12	0.58	0.12	0.90
12	Ni	0.95	0.14	1.28	0.15	2.66	0.21	1.88	0.18	0.76	0.13	1.51
13	Cu	10.86	0.53	10.51	0.52	14.33	0.67	5.95	0.34	9.49	0.48	10.23
14	Zn	76	3	188	8	155	6	52	2	138	6	122
15	Br	2.99	0.22	2.05	0.18	6.05	0.34	2.27	0.19	2.31	0.19	3.13
16	Rb	24.11	1.06	6.86	0.37	15.66	0.73	16.90	0.78	12.23	0.59	15.15
17	Y	24.82	1.09	1.13	0.15	1.72	0.17	6.93	0.38	0.69	0.13	7.06
18	Sb	0.33	0.11	0.07	0.10	0.38	0.12	0.04	0.10	0.14	0.11	0.19
19	Ba	2.22	0.19	23.39	1.04	20.05	0.90	3.17	0.23	21.44	0.96	14.05
20	Pb	4.77	0.29	5.49	0.32	6.81	0.37	4.68	0.29	2.83	0.21	4.92
21	U	3.12	0.27	1.67	0.15	1.21	0.11	1.47	0.13	1.95	0.17	1.88

Table 3

The concentration of chemical elements in the active moss (mg/kg)

No.	Sample	LD01		LD02		LD03		LD04		LD05		Mean
	Ele.	Con.	± ∆	Con.	± ∆	Con.	± ∆	Con.	± ∆	Con.	± ∆
1	Al	1580	110	1613	113	3363	235	1327	93	1277	89	1832
2	Si	2995	170	5335	276	10831	580	4522	245	4284	229	5593
3	P	227	17	731	55	566	43	357	27	432	33	462
4	S	448	29	1134	73	1160	75	725	47	1044	67	902
5	Ca	843	47	804	45	799	44	723	40	794	44	793
6	Ti	79	6	91	7	139	11	133	11	80	6	104
7	V	4.64	0.41	5.73	0.51	4.39	0.39	6.36	0.56	3.43	0.30	4.91
8	Cr	4.81	0.31	4.99	0.32	9.32	0.60	9.01	0.58	4.86	0.32	6.60
9	Mn	106	7	54	4	76	5	39	3	48	3	65
10	Fe	3000	237	1826	144	3279	259	1693	134	1506	119	2261
11	Co	1.30	0.08	0.66	0.04	1.13	0.07	0.47	0.03	0.56	0.04	0.82
12	Ni	0.83	0.06	1.13	0.08	2.27	0.15	1.44	0.10	0.69	0.05	1.27
13	Cu	11.79	0.65	11.45	0.63	15.10	0.83	5.62	0.31	10.62	0.59	10.91
14	Zn	81	5	200	11	159	9	48	3	151	9	128
15	Br	3.55	0.18	2.44	0.12	6.98	0.35	2.35	0.12	2.83	0.14	3.63
16	Rb	16.30	1.45	4.65	0.41	10.27	0.91	9.94	0.88	8.52	0.76	9.93
17	Y	16.38	1.49	0.75	0.07	1.10	0.10	3.98	0.36	0.47	0.04	4.54
18	Sb	0.18	0.02	0.04	0.00	0.20	0.02	0.02	0.00	0.08	0.01	0.10
19	Ba	2.19	0.13	23.13	1.41	19.18	1.17	2.72	0.17	21.77	1.32	13.80
20	Pb	3.75	0.29	4.33	0.33	5.19	0.40	3.20	0.24	2.29	0.17	3.75
21	U	3.39	0.19	1.82	0.10	1.27	0.07	1.39	0.08	2.18	0.12	2.01

TXRF measurement samples were conducted on an S2 PICOFOXTM spectrometer. The measuring time was 600 seconds per sample. The fit quality is a statistical parameter, which allows conclusions about the quality of the deconvolution. The standardized square sum of the differences between the measured and the calculated, deconvoluted intensities is calculated for all channels. Preferably, the value for the fit quality should be less than 10. High values (>10) indicate misidentified or non-identified elements respectively for an inaccurate gain correction. The following function is used to fit the following equation:

where n is the first channel of the peak i (the left channel); n is the end channel of the peak i (the right channel); y the counts of channel i+1; y the counts of channel i.

where δ is the standard deviation for the peak area; N is net peak area for the element i; N is the background area.

The TXRF method has identified 21 elements, including Al, Si, P, S, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Rb, Y, Sb, Ba, Pb, and U. Figure 5,Table 2 and Table 3 present the measurement results.

DISCUSSION

The chemical elements deposited in the air were conducted by two methods: native moss and active moss in Lac Duong town (Lam Dong Province). The results showed that:

CONCLUSION

This study used moss bags and native moss to investigate the deposition of chemical elements in the air in Lac Duong town. The results of analysis by TXRF technique identified 21 elements. The results showed that the concentration of element deposition in the Lac Duong atmosphere was quite low compared to other studies in a few big cities in Vietnam.

This method can be applied through the moss bag technique when making biological observations to survey the air-deposited elements in the urban area – where there is a lack of native moss, or where native moss is difficult to grow. Because of low cost, this technique is also suitable for the assessment of air quality, regardless of environment, location, or topography. Additionally, it is very convenient to build environmental monitoring networks to have an overview of future environmental change.

COMPETING INTERESTS

The authors commit that they have no competing interests.

ACKNOWLEDGEMENTS

This research is supported by Dalat University under the project from 2021.

AUTHORS CONTRIBUTIONS

L. H. Khiem proposed the experimental plan, implemented the experiment. N. A. Son, N. T. M. Sang performed the experiments and literature review, compiled the data and manuscript preparation.

VNUHCM Journal of

Science and Technology Development

Comparison of moss bag and native moss technique in monitoring airborne particulate and toxic elements

Online metrics

Statistics from the website

Statistics from Dimensions

Statistics from PlumX

Abstract

INTRODUCTION

Materials — Methods

Sampling area

Native moss preparation

Moss bag preparation

TXRF technique

RESULTS

DISCUSSION

CONCLUSION

COMPETING INTERESTS

ACKNOWLEDGEMENTS

AUTHORS CONTRIBUTIONS

Comments