Detection of Heavy Metals in Honey Samples using Inductively Coupled Plasma Mass Spectrometry

 

Abstract

Honey is a composite mixture of various carbohydrates, enzymes, flavonoids and organic acids. It is used for a wide variety of purposes and is a known antimicrobial agent. Heavy metals may be present in trace quantities in honey and their detection is important for the quality control of honey and it also serves as an indicator of environmental pollution. For this study, eight samples of honey were collected from New Delhi. Using inductively coupled mass spectrometry (ICP-MS), the honey samples were tested for the presence of seven elements – Copper, Zinc, Arsenic, Cadmium, Mercury, Tin, and Lead.

Introduction

According to the Codex Alimentarius, honey is defined as the “Honey is the natural sweet substance produced by honey bees from the nectar of plants or from secretions of living parts of plants or excretions of plant sucking insects on the living parts of plants, which the bees collect, transform by combining with specific substances of their own, deposit, dehydrate, store and leave in the honey comb to ripen and mature.” [1]
Honey is a composite mixture of carbohydrates such as fructose, glucose, sucrose, and maltose; enzymes such as invertase and amylase; vitamins; minerals; flavonoids and organic acids.[2] Due to its highly unique and complex chemical nature, honey finds a host of applications as a sweetener and antimicrobial agent. It is also used extensively for the treatment of burns, wounds, and skin ulcers.[3]
To fulfill all these roles, it is important for honey to be free from contamination. One source of contamination, examined by this paper, is the presence of heavy metals such lead, cadmium, arsenic, and mercury. Detection of heavy metals in honey serves a necessary purpose in quality control and in monitoring of bee environments. Heavy metals, if present in significant amounts, adversely impact human health and signal contamination of bee environments.
Hairy bodies of bees gather heavy metals from the atmosphere and bring them back to the hive with pollen. In addition, the heavy metals may be absorbed by the bees together with the nectar of the flowers or through water and honeydew. Polluted soil may lend heavy metals to the flower nectar as these may be absorbed by the roots of plants from contaminated soils. Consequently, the presence of heavy metals in honey can be seen as a valuable indicator for environmental contamination. [4]
The use of trace elements such as copper, cadmium, lead, mercury, and zinc is prevalent in the human economy. Due to expansive industrial growth, heavy metals have become common environmental pollutants. In honey, particularly, these metals originate from external sources such as industrial smelter pollution, industrial emissions and unsuitable procedures during the different stages of honey production. In addition, the origin of metals in honey may be agrochemicals such as organic mercury, cadmium-containing fertilizers and arsenic-based pesticides.[5]
Elements such zinc, iron, and copper are vital micronutrients for humans and are needed in adequate amounts to maintain normal growth and development. Their deficiency is linked to impairment in cognitive performance, lowered work capacity, lowered immunity to infections, and pregnancy complications. However, elements such as lead and arsenic have little to no known requirements in the human diet. In fact, exposure to these elements is toxic as these trace elements damage human metabolism and have known cytotoxic and carcinogenic effects.[6]
The maximum permissible limit of heavy metals in food in India is prescribed by the Prevention of Food Adulteration (PFA) Act of 1955. Rule 57 states the limits of contaminants under the category “Foods Not Specified”, which includes honey.

Table 1: PFA Heavy Metal Limits

Method

Sample Collection
Eight samples of honey were collected from the local markets of New Delhi. The samples were collected in airtight glass containers and stored in room temperature in a lightless place till analysis.
Sample Preparation
1.0g of each sample of honey was digested in a microwave digester with 5.0ml concentrated 65% nitric acid and 1ml 30% hydrogen peroxide. The instrumental parameters and settings for the microwave digester were 120°C and 700 Psi for the first ten minutes and 130°C and 800psi for the next fifteen minutes. The sample was then filtered using a filter paper with a pore size of 0.45 microns and diluted up to 20ml with deionized water.
ICP-MS
An Agilent 7500ce ICP-MS with an Octopole Reaction System and standard sample introduction system (Nickel cones, glass concentric nebulizer, a quartz Peltier cooled spray chamber and quartz torch) was used for elemental analysis.
The following operating conditions were used:

Table 2: ICP-MS Operating Conditions
Elemental analysis was carried out by inductively coupled plasma mass spectrometry (ICP-MS) after microwave-assisted acid digestion. All glassware used for the analysis was cleaned with 10% HNO₃ solution and rinsed with ultrapure water. The concentrations of seven elements (Cu, Zn, As, Cd, Hg, Sn, Pb) were determined in honey samples. All samples were measured in triplicate by the ICP-MS.

Results

Discussion

In the present study, all the eight samples showed the presence of lead. Lead was found in quantities ranging from 0.532 ppm to 4.237 ppm. Two samples were contaminated with high concentrations of lead, which exceeded the maximum permissible limit of 2.50 ppm as prescribed by the PFA Rules. Lead, a highly toxic presence in foodstuff, has been linked to high blood pressure, heart disease, kidney disease, and reduced fertility. Overexposure to lead in infants can also lead to severe damage to brain development. High concentrations of lead in honey might be because of pollution from the vehicular traffic, heavy industries, and other anthropogenic activities. [7]
Mercury was detected, albeit in small quantities, in six out of the eight samples tested and ranged from 0.075 ppm to 1.124 ppm. In one of the samples, the concentration of mercury was 1.124 ppm, which was beyond the permissible limit of 1.0 ppm. Excessive exposure to mercury is deleterious to human health. The brain remains the target organ for mercury, yet it can impair any organ and lead to malfunctioning of nerves, kidneys and muscles. [8]
In one of the samples, the concentration of arsenic detected was 1.392 ppm. This was above the permissible limit of 1.1 ppm as set by the PFA. Since arsenic is a known carcinogenic, strict attention must be given to regulate its presence in honey. The principal causes for presence of arsenic in honey include non-ferrous metallurgy, and agrochemicals such as fertilizers and arsenic-based pesticides. Arsenic is also present in the soil, water, and air and hence may be absorbed by plants from these sources, consequently contaminating honey. The presence of arsenic beyond the permissible limits in honey samples is an indicator of micro pollution and hence, the use of arsenic-based fertilizers should be checked to limit environmental pollution.[9]
Micronutrients zinc and copper were detected in all of the eight samples. Zinc and copper and essential for several functions of the body such as regulating the metabolism. Moreover, copper acts as an antioxidant whereas zinc is required for the proper functioning of the immune system. The presence of copper and zinc in honey were beneath the maximum permissible limits in all samples, indicating that there is scarce possibility of zinc or copper poisoning due to consumption of honey.
Cadmium was detected in seven out of eight samples and its concentration ranged from 0.022 ppm to 0.481 ppm. Tin was detected in all samples. Like cadmium, tin contamination did not exceed the permissible limits in any of the samples. Cadmium and tin are released into the environment through numerous industrial processes and enter the food chain through contaminated soil and water. Hence, cadmium and tin concentrations in different places depend on many factors, explaining the variability in the concentration of tin and cadmium tested in the honey samples.

Conclusion

Eight samples of honey were collected from New Delhi and were tested for the presence of seven elements – Copper, Zinc, Arsenic, Cadmium, Mercury, Tin, and Lead –using ICP-MS. Two samples contained quantities of lead that exceeded the maximum permissible limit set by the Prevention of Food Adulteration Act of India. Arsenic was found exceeding the maximum limit in one sample and mercury in another. Copper, zinc, cadmium, and tin were present well below the limits.
The presence of heavy metals in honey is an indicator of environmental pollution. Sufficient care must be taken to regulate the amount of heavy materials entering the environment as exposure to these elements can adversely affect human health.

References

1. Codex Alimentarius Commission, “Revised Codex Standard for Honey,” Codex STAN 12-1981, Rev. 1 (1987), Rev. 2 , 2001.

2. J.W. White, Jr. and Landis W. Doner, “Honey Composition and Properties”, Beekeeping in the United States, Agricultural Handbook Number 335
3. Stefan Bogdanov, Tomislav Jurendic, Robert Sieber, Peter Gallmann,“Honey for Nutrition and Health: a Review”, American Journal of the College of Nutrition, 2008, 27: 677-689
4. Chandrama Singh, Shubharani, R and Sivaram, V, “Assessment of Heavy Metals in Honey by Atomic Absorption Spectrometer’’, World Journal of Pharmacy and Pharmaceutical Sciences, Volume 3 Issue 8
5. Pisani A, Protano G, Riccobono F. “Minor and trace elements in different honey types produced in Siena county (Italy)”, Food Chem. 2008;107:1553–60.
6. K.O. Soetan, C.O. Olaiya, O.E. Oyewole, “The importance of mineral elements for humans, domestic animals and plants: A review”, African Journal of Food Science Vol. 4(5) pp. 200-222, May 2010
7. Podgorski W, Kanoniuk D,“Honey as marker of environmental contamination with heavy metals”, Section EE Zootechnica 2004; 22(3): 17-24
8. Monisha Jaishankar, Tenzin Tseten, Naresh Anbalagan, Blessy B. Mathew, and Krishnamurthy N. Beeregowda, “Toxicity, mechanism and health effects of some heavy metals’’
9. Hasan Mohammadi Aghamirlou et al, “Heavy metals determination in honey samples using inductively coupled plasma-optical emission spectrometry”

About the Author

Ishana Aggarwal, 18, India

Born and brought up in New Delhi, Ishana Aggarwal currently studies science in Modern School Barakhamba Road, New Delhi as a high school senior. In addition to chemistry, her interests  include literature and music.