The objective of the present study was to investigate trace metal levels of different varieties of fresh water fish using Inductively Coupled Plasma Mass Spectrophotometer after microwave digestion (MD-ICPMS). Fish samples were collected from the outlets of twin cities of Hyderabad and Secunderabad. The trace metal content in different varieties of analyzed fish were ranged from 0.24 to 1.68 mg/kg for Chromium in
Trace elements are found naturally at various levels in the hydrosphere, and many are required for physiological and metabolic processes of organisms [
Trace elements are generally classified as either essential elements (Zn, Se, Cu, I, Mo, and Cr) or probably essential (Mn, Si, Ni, Bo, and Va). However both deficiency and excess intake of essential elements can be detrimental to human health. As top predators, fish may be the end reservoir of the bioaccumulation of trace elements in a food chain, causing them to be potentially hazardous to consume [
Fortunately previous studies reveal that the trace metal concentration level in fishes is not that much alarming in South East Asian countries. The researchers have examined muscles, livers, and gills of fishes as these organs play different roles in bioaccumulation process [
In modern human nutrition, fish and fishery products have attracted considerable attention since they exhibit unique nutritional benefits for human health. It is well known that fish is one of the major sources of animal protein and has been widely accepted as a good source of other essential elements for the maintenance of a healthy body [
The uptake of trace metals in fish occurs through food ingestion and water via the gills. Fish farming is the main activity in global aquaculture, a sector that has witnessed a steady increase in the past 15 years [
India is one of the leading countries in terms of fish, aquaculture, and marine food resources [
Over the last few decades, there has been growing interest in determining trace metal and heavy metal contents in fresh water and marine environment and attention was drawn to the measurement of contamination levels in public food supply particularly in fish. Toxicological and environmental studies have prompted interest in the determination of trace metals and toxic elements in foods. Several reliable analytical methods were available for monitoring trace metals levels in fresh water and marine food samples, but Inductively Coupled Plasma Mass Spectrometer (ICP-MS), being the most sophisticated and reliable technique, was widely used for determination and quantification of trace metals in food samples. This study is focused on measuring the concentration level of selected metals (Mn, Zn, Cr, Co, Cu, and Se) in different species of fishes collected from twin cities of Hyderabad and Secunderabad. Moreover, proximate composition along with length and weight of the fish were also investigated to assess whether these fish were acceptable for human consumption.
All chemicals used were analytical grade quality. Ultrapure water was obtained from a Millipore water system (Millipore), ultrapure Nitric acid (HNO3, Merck) was used to digest the samples. Stock standard solutions of Chromium, Manganese, Cobalt, Copper, Zinc, and Selenium containing 10
Selected varieties of fresh water fish were collected from local markets of twin cities of Hyderabad and Secunderabad, Andhra Pradesh, India. The targeted species were commercial fish and shellfish available to consumers in Hyderabad. In the present study, fish and shellfish samples were collected by stratified random sampling procedure. This approach is the most suitable method for generating food composition database [
The fish samples were beheaded, gutted, washed, and filleted. The primary sample of each species was used to prepare a composite sample. Special care was taken to prevent metal contamination of the samples. All laboratory ware were soaked in 2 M HNO3 for 48 h and rinsed several times with distilled water and deionized water prior to use. Small size fish were pulverized with skin and the edible portion weight was recorded. Aliquots of edible tissue was taken for analysis of trace metals and proximate composition and stored in a freezer at −20°C till further analysis.
The closed vessel microwave digestion system (CEM-MARS-USA) was used to digest homogenized fish samples (between 0.5 and 1.5 g) and placed in a Teflon digestion vessel with 3 mL of ultrapure HNO3 and 1 mL of hydrogen peroxide (H2O2-Merck). Sealed containers were placed in a microwave oven and heated according to the digestion program (program: power, 1600 W (100%); ramp time, 15 mins; temperature, 200°C; hold time, 15 mins; and cooling time, 15 mins). After digestion, sample solutions were cooled to room temperature then transferred quantitatively into acid cleaned 25 mL standard volumetric flasks and made up to 25 mL with double distilled deionized water and prepared under the same conditions as the calibration standards in 6% (v/v) HNO3. A blank digest was carried out in the same way [
Chromium, Manganese, Cobalt, Copper, Zinc, and Selenium in fresh water fish were analyzed using ICP-MS (PerkinElmer Élan 9000-USA). For better operating conditions the ICP-MS was adjusted to nebulizer gas flow 0.91 L/min, radio frequency (RF) 1200 W, lens voltage 1.6 V, cool gas 13.0 L/min, and auxiliary gas 0.70 L/min [
ANOVA was employed to test the difference between means of various fishes with regard to trace metals.
The weight and length of the available varieties of fresh water fish and shell fish were shown in Table
List of fresh water fish collected from markets with a narrow range of weight and length.
Local name | Common name | Scientific name | Edible portion/kg | Weight (Kg) |
Length (cm) |
---|---|---|---|---|---|
Bommidayalu | Channa marulius |
|
733 | 0.10–0.25 | 10–25 |
Ravva | Roho labeo |
|
632 | 0.50–3.20 | 15–35 |
Chanduva | Pomfret white |
|
630 | 0.30–1.50 | 13–35 |
Nallasandawah | Pomfret black |
|
644 | 0.30–1.50 | 13–35 |
Jallalu | Cat fish |
|
720 | 0.10–0.20 | 15–25 |
Chandamama | Silver pomfret |
|
621 | 0.05–0.15 | 10–25 |
Bangaru teega | Gold fish |
|
587 | 0.50–2.00 | 10–30 |
Korramenu | Soleole |
|
698 | 0.50–3.50 | 15–35 |
Royya | Tiger prawn |
|
570 | 0.10–0.30 | 05–15 |
Royya | Scampi prawn |
|
408 | 0.10–0.20 | 05–15 |
Proximate content of moisture, ash, and fat contents was determined using Association of Official Analytical Chemists [
Proximate composition of fresh water fish was as shown in Table
Proximate composition in fresh water fish—g%.
Local name | Scientific name | Moisture | Ash | Protein | Fat |
---|---|---|---|---|---|
Bommidalu |
|
|
|
|
|
Ravva |
|
|
|
|
|
Pomfret-White |
|
|
|
|
|
Pomfret-Black |
|
|
|
|
|
Jallalu |
|
|
|
|
|
Chandamama |
|
|
|
|
|
Gold fish |
|
|
|
|
|
Korramenu |
|
|
|
|
|
Tiger prawn |
|
|
|
|
|
Scampi prawn |
|
|
|
|
|
Values are mean ± SD,
ICP-MS method was standardized and validated using certified reference material (CRM) purchased from National Institute of Standard Technology (NIST). Recoveries of trace metal contents in the present study were shown in Table
Recovery study using certified reference material (CRM)—mg/kg.
Element | Analyzed value | NIST-certified value | % of recovery |
---|---|---|---|
Cobalt |
|
|
100 |
Chromium |
|
|
95 |
Copper |
|
|
103 |
Manganese |
|
|
99 |
Selenium |
|
|
106 |
Zinc |
|
|
100 |
Values are mean ± SD,
NIST: National Institute of Standard Technology.
Trace metal content in fresh water fish—mg/Kg.
Scientific name | Chromium | Manganese | Cobalt | Copper | Zinc | Selenium |
---|---|---|---|---|---|---|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Values are mean ± SD,
When fish are exposed to elevated metal levels in an aquatic environment, they can absorb the bioavailable metals directly from the environment via the gills and skin or through the ingestion of contaminated water and food. Metals in the fish are then transported by the bloodstream which brings it into contact with the various organs and tissues [
Joint FAO/WHO Expert Committee on Food Additives recommends that for an average adult (60 kg body weight), the provisional tolerable daily intakes (PTDI) of copper is 3 to 4 mg and Zinc is 60 mg, respectively. The Zn level permitted for fish is 50 mg/kg, according to Turkish Food Codex. According to WHO the maximum tolerable levels of Selenium are 50 to 150
In the present study the trace metal levels conform to FAO/WHO and the literature published values in fresh water fish except Selenium. However the estimated Se levels were higher in our samples than WHO/FAO recommended levels and those reported in the literature. The investigation of trace metals in fresh water fish demonstrated that Zn is the highest concentration in fish muscle followed by Cu, Mn, Se, Cr, and Co. It is known that a variation in the mineral composition of marine foods is closely related to seasonal and biological differences (species, size, dark/white muscle, age, sex, and sexual maturity), area of catch, processing method, food source, and environmental conditions. This study provides information on trace metal concentrations of fresh water fish consumed in twin cities of Hyderabad and Secunderabad and therefore provides an essential baseline data with which future levels may be compared and evaluated. Apart from other benefits, the data of the present study are also extremely useful to the scientific community and public officials involved in health risk assessment and management of environmental contaminants as well as a guide to the best course of action to restore ecosystems and, in turn, to preserve human health. However, it is just a selective fish investigation; metal contamination levels should be carefully monitored on a regular basis in more fish species, to detect the change in their accumulation patterns.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors are grateful to Dr. B. Sesikeran, Director, National Institute of Nutrition, Hyderabad, for encouragement and facilities provided. The authors would also like to thank the staff of the Microwave and ICP-MS laboratory for their extended assistance.