Environmental Impact of Heavy Metals

Abstract

Heavy metals cause toxicity in biological systems by bonding to Sulfhydryl groups and producing reactive oxygen species (ROS). Many international organizations established a standard regarding the presence of heavy metals in the environment, food, and drinking water as a result of numerous harmful effects on humans and animals observed. This study aimed to determine the level of heavy metal concentrations and water quality in the Romi River, where some heavy metals concentrations (Iron 0.89 mg/L and Nickel 0.36 mg/L) exceeded the WHO maximum standard limits (Nickel 0.02 mg/L and 0.030 mg/L). The mean concentrations of the metal’s chromium, iron, nickel, and zinc with standard deviation were found to be: 0.100.1 mg/L, 0.890.1 mg/L, 0.060.1 mg/L, and 0.200.1 mg/L, respectively. This study revealed that the contamination occurs as a results of effluents release into the river thereby causing many harmful effect to the community around them.

1. Introduction

Water pollution occurs in both rural and urban areas in Nigeria. Many factories in Nigeria are located on river banks and use the rivers as open sewers for their effluents. It is important to note that some of these heavy metals are required for proper biochemical function. Metals such as lead, chromium, and arsenic, on the other hand, can be toxic when consumed in small or large amounts. In general, the ionic form of a metal is more toxic because it can form toxic compounds with other ions. Electron transfer reactions with oxygen can produce toxic oxyradicals [1, 2].

Water contamination endangers other resources, such as fisheries, and land resources, for example, have already suffered significantly. The majority of environmental pollution is caused by anthropogenic sources, specifically domestic and industrial activities [1, 2]. Failure to halt further deterioration of environmental quality may jeopardize the health of a large proportion of the population, with serious political and socioeconomic consequences [3, 4].

Heavy metal exposure has increased as a result of anthropogenic, industrial, and agricultural activity as well as modern industrialization, all of which have negative impacts on human health. The environmental concern of hazardous metal contamination of water and air affects hundreds of millions of people worldwide. Heavy metal pollution in food is a problem for both human and animal health. In this context, the concentration of heavy metals in air, food, and water sources is evaluated [3]. Among the numerous toxins in the environment, metals can exist naturally and stay in the ecosystem. As a result, human exposure to metals is unavoidable, and some researchers have found that the toxicity of metals varies depending on gender [4]. Biological systems may typically react to them by losing one or more electrons, releasing metal cations that are affine to the nucleophilic sites of essential macromolecules. Several acute and long-term harmful effects of heavy metals have an impact on several human organs. Examples of the adverse effects of heavy metal toxicity include cancer, gastrointestinal and kidney dysfunction, nervous system diseases, skin lesions, vascular damage, immune system malfunction, and birth defects. The cumulative effects of simultaneous exposure to two or more metals have been reported [5, 6, 7].

Heavy consequences such abdominal cramping, bloody diarrhea, and kidney failure can occur after exposure to high doses of heavy metals, especially lead and mercury [5, 6]. Contrarily, low-dose exposure poses a subtle and unnoticed risk unless it is consistently experienced, at which point its side effects, such as neuropsychiatric illnesses characterized by exhaustion, anxiety, and negative effects, may be identified.

2. Research review

2.1 Toxic effect of some heavy metals

Out of the 92 naturally occurring elements, 30 are recognized to be potentially harmful to humans. These are created by anthropogenic or natural processes, but the industrial discharge that is of concern in this case is of particular note [7]. Additionally, it is well recognized that the heavy metal pollution chain moves in a circular pattern from industry to atmosphere to soil to water to food to people. Heavy metals can be harmful even at relatively low levels, despite the fact that toxicity is a function of concentrations. The importance of human exposure, consumption, and absorption was emphasized, particularly in industrialized nations.

2.2 Chromium (Cr)

One of the heavy metals whose concentration continually rises as a result of industrial expansion, particularly the growth of the chemical and tanning industries, is chromium. Electroplating, leather tanning, wood preservation, pulp processing, steel manufacture, and many other operations release chromium into the environment, and the concentrations of chromium and nickel in the environment vary greatly. The greater use of these two metals in emerging nations and their non-degradability raise serious concerns [1]. The human body is carcinogenic and highly soluble in hexavalent chromium. It is also well known that the metallurgies, refractory, chemical, and tannery sectors employ this same hexavalent chromium extensively.

2.3 Iron (Fe)

A heavy metal in the first row of transition metals, iron is one of them. Although Fe²⁺ is also detected, Fe³⁺ is the main form that is seen. Iron serves as an oxidizing and reducing agent in the porphyrin enzyme of respiration (Vines and Rees).

Seawater contains roughly 3.5 ppm of iron, the fourth most prevalent element in the earth’s crust [1]. It reacts fairly quickly. The transition metal (heavy metal) iron is by far the most common and significant one that has a purpose in living systems. Proteins that contain iron take part in the transport of oxygen and the transfer of electrons, respectively. There are other molecules, [4] whose job it is to transmit and store iron. Ferritin and albumin serve as the storage proteins in humans and many other higher animals.

2.4 Nickel (Ni)

Nickel is the most useful element in soil and plant research. Nickel appears to be required for the growth of marine micro algae. The effect of food containing very low concentrations of nickel (e.g., 40.00 ug/g) includes impaired liver metabolism, decreased iron absorption, and decreased activity of many enzymes. The average concentration of nickel in the world’s soil is 40.00 mg/g [7]. In the absence of the emission effect, dietary nickel intake was estimated to be 16,511 ug/day on average [8].

The toxicity of nickel is determined by the route of exposure and the solubility of the nickel compound. Epidemiology studies have shown that occupational inhalation exposure to nickel (Ni) dust can result in an increase in pulmonary and nasal cancer [9].

2.5 Zinc (Zn)

Zinc is a heavy metal in the periodic table’s first row of transition metals. Zinc is found everywhere and has been shown to be a growth factor in plants and some rodents. Its absence causes mottled leaf disease in fruit trees. Zinc is found in mammalian enzymes such as carbonic anhydrase. It is required for protein metabolism and appears to be involved in the production of chlorophyll in some way. Zinc is essential for plant growth due to its role in auxin formation and as a component of certain enzymes [9]. Zinc is required for the synthesis of the molecule tryptophan, from which auxin is produced.

Several crop disorders were reported in the early 1900s that have now been identified as zinc deficiencies [9]. A thorough investigation of zinc deficiency in all plants reveals, among other symptoms, some form of leaf chlorosis, mostly on veins and ranging in color from white to light green.

Zinc deficiency is common in soils with abnormally high levels of soluble or total phosphates. An early study on Tung’s tree zinc deficiency in fluoride concluded that high phosphate in soils was an important factor reducing available zinc [10]. A relatively low concentration of the element in the body can cause heavy metal toxicity, most commonly intestinal distress.

3. Environmental pollution

Through their bonds with sulfhydryl groups and the production of ROS, heavy metals cause toxicity in biological systems. In addition to oxidative stress and glutathione depletion, this results in the inactivation of important macromolecules. There are a number of events that take place once hazardous metals enter the body and are exposed to them, including interactions with or inhibitions of certain metabolic pathways [10, 11]. Multiple negative consequences on both people and animals are consequently seen. Congenital disorders, immune system problems, hormone changes, particular organ dysfunctions, metabolic abnormalities, cancer, and congenital disorders are a few of these [11]. The presence of metals in the environment, food supply, and drinking water is therefore regulated by a number of international organizations. Studies on risk assessment examine if heavy metals are present in food and water. Nearly 21% of them had amounts that could be detected, it was discovered.

4. Solubility of metals and metal compounds

Chemical speciation affects the environment’s metal and metal compound solubility, bioavailability, and persistence; for some metals, speciation may affect the pattern of toxicity (e.g., inorganic arsenic versus organic compounds, inorganic and organic mercury compounds). The papers on exposure concerns and bioavailability and bioaccumulation explore the function of speciation in bioavailability and bioaccumulation within the environment as well as bio-accessibility to human receptors. It is typically believed that the potential toxicity of inorganic species is connected to the cat-existence ions in bodily tissues (in most cases, bound to a tissue ligand). The potential or availability of the metal for interacting at a particular biological target, such as may depend on the intracellular environment and kind of ligand or protein binding [2].

Solubility is one of the most important factors influencing metal and metal compound bioavailability and absorption. A metal compound’s solubility is determined by its chemical species, the pH of its medium (H+ ions), and the presence of other chemical species in the medium (see the environmental chemistry paper) [12]. Except for silver, mercury, and lead, nitrates, acetates, and all chlorides of most metals are soluble. Except for barium and lead, most metal sulphates are also soluble. Most hydroxides, carbonates, oxalates, phosphates, and sulphones, on the other hand, are poorly soluble. Particle size is another factor that influences the absorption of poorly soluble compounds: fine particles are usually more soluble. Metallic lead in body tissues (as may occur after gunshot wounds) is most likely absorbed [2].

5. Measures of exposure to metals

In terms of health assessment, the extent of a metal’s exposure is best determined by measuring its internal concentration, and even better, the biologically effective dose at the target organ (as opposed to environmental concentration). However, for a variety of reasons, determining the internal or biologically effective dose of the metal at the target tissue is not always feasible. For example, the activity of the heme-synthesizing enzyme aminolaevulinic acid dehydrate (ALAD) in red blood cells is directly related to blood lead concentration and thus may be used as a surrogate for blood lead measurement. The use of biological indicators or markers of exposure, also known as “biomarkers of exposure, “ is a method of linking a person’s external exposure [13].

5.1 Material

Polyethylene (plastic) bottles, 14 volumetric flasks (100.00 ml), glass funnel, filter paper, 14 beakers (500.00 ml), hot plate pipette, measuring cylinder, hydrochloric acid (HCl), nitric acid (HNO₃), Atomic Absorption Spectroscopy (AAS), Conductivity Meter, Turbidity Meter, and pH Meter were used for the analysis.

5.2 Methods

To avoid the risk, the sample was prepared and digested using standard analytical methods with nitric acid (HNO3) and hydrochloric acid (HCl) at relatively low temperatures, as reported by [1].

The powerful solvent used was aqua regia, a mixture of hydrochloric acid and nitric acid (10:1 V/V). 100.00 ml of each sample was measured and transferred to a 500.00 ml beaker, followed by 10.00 ml of hydrochloric acid (HCl) and 1.00 ml of nitric acid (HNO3). The mixture was then heated on a hot plate for about 3 hours at a relatively low temperature (200C-500C) (NB: Do not allow it to boil) until it was reduced to about 20.00 ml.

The mixtures were then cooled and filtered in a 100.00 ml volumetric flask using a glass funnel and filter paper, and then diluted to volume (i.e., distilled water was added to the mark of the volumetric flask).At the quality control laboratory, the mixtures were tested using Atomic Absorption Spectroscopy (AAS). Based on the above procedure, we reanalyzed the five different samples for the following heavy metals: chromium (Cr), iron (Fe), nickel (Ni), and zinc (Zn).

6. Results and discussion

6.1 Discussion

Table 1 shows the conductivity values for January samples analyzed at five different points: 593.00, 618.00, 828.00, 507.00, and 690.00 μohms/cm. The conductivity values were generally greater than the WHO maximum permissible limit of 500.00 μohms/cm. This is evident from the measured mean of 647.20 ohms/cm. Point 3 had the highest conductivity of 828.00 μohms/cm, while point 1 had the lowest conductivity of 593.00 μohms/cm. Furthermore, when compared to the other points, the conductivity at point 4 (507.00 μohms/cm) was slightly higher than the WHO standard limit.

Table 2 shows the conductivity (μohms/cm) values for February samples analyzed at five different points: 511.00, 499.00, 497.00, 500.00, and 513.00 μohms/cm. In comparison to the mean of 504.00 μohms/cm recorded, the conductivity values were generally greater than the maximum value of 500.00 μohms/cm of WHO standards limits. Points 5 and 1 had the highest conductivities of 513.00 μohms/cm and 511.00 μohms/cm, respectively, while points 3, 2, and 4 were all within the WHO standard limits.

The pH values for January, February, and March samples at five different points are as follows: 7.60, 6.53, 7.52, 6.89, 6.50, 6.66, 6.86, 6.56, 6.76, 6.84, 6.93, 7.10, 7.09, 7.25, and 7.06, as shown in Tables 1 and 2. The pH values were found to be generally within the WHO acceptable limits of 6.50–9.20. This is evident from the mean pH value of 7.01, which falls within the WHO threshold range of 6.50–9.20. This implies that the effluent discharged into the river by Kaduna Refining and Petrochemical Company has no effect on the river’s pH concentration.

The temperature values recorded for the five different samples over three consecutive months (January, February, and March) at five different points are as follows: 21.30, 20.80, 20.20, 20.90, 20.30, 20.80, 20.50, 20.40, and 20.70°C, which are all less than the room temperature of 25.00°C. While those of March were 27.60, 29.30, 29.80, 30.10, and 30.00°C higher than the room temperature, as shown in Tables 1–3. The mean temperature values of 20.80°C, 20.54°C, and 29.36°C demonstrate this. The increase in temperature values observed in March could be attributed to seasonal changes rather than Kaduna Petrochemical and Refining Company’s activities.

As shown in Table 1, the turbidity values for January samples at five different points are: 28.70, 14.45, 43.69, 103.00, and 14.01 NTU, which are higher than the maximum limits of WHO and Federal Environmental Protection Agency (FEPA) acceptable standards of 10.00 NTU. Considering the recorded mean turbidity value of 40.77 NTU, which is significantly higher than the acceptable value.

As shown in Table 2, the turbidity values for February samples at five different points are: 26.35, 18.36, 23.85, 25.93, and 31.93 NTU, which are higher than the maximum limits of WHO and Federal Environmental Protection Agency (FEPA) standard acceptable standards of 10.00 NTU. Taking into account the recorded mean turbidity value of 25.28 NTU, which is higher than the acceptable value.

The turbidity values for March samples at five different points, as shown in Table 3, are greater than the maximum limits of WHO and Federal Environmental Protection Agency (FEPA) standard acceptable standards of 10.00 NTU. Considering the recorded mean turbidity value of 34.16NTU, which is significantly higher than the acceptable value. As a result, the increase in mean turbidity values of 40.77, 25.28, and 34.16 NTU above the acceptable standard in January, February, and March could be attributed to effluents released by the Kaduna Petrochemical and Refining Company.

6.2 Chromium (Cr)

The amount of chromium (Cr) in the five (5) different samples at different points in January, February, and March samples was less than 0.0100 mg/kg (<0.0100 mg/L), as shown above. This is evidence from the mean (<0.0100), standard deviation (0.0112), and variance (0.0001), which show how far apart each metal is from its arithmetic mean. The coefficient of correlation between the three (3) months was discovered to be zero (0), indicating that there was no correlation between them. The WHO and FEPA drinking water standards were 0.05–2.00 mg/L (Table 4).

6.3 Iron (Fe)

The iron (Fe) content of these five samples at various points is shown in Table 5 for January samples in mg/L. At point 1, the amount is high, but at point 2, the amount decreases, while at point 3, the amount increased dramatically, and at point 4, the amount was very low, while at point 5, the amount decreased dramatically.

For February samples, the amount decreases at points 1, 2, and 3, but increases slightly higher at point 4, and dramatically increases at point 5.

For March samples, the amounts at points 1, 2, 3, and 4 decrease, but the amount at point 5 increases to be greater than the amounts at points 3 and 4 but less than the amounts at points 1 and 2. This is evidenced by the three-month mean of 0.2587, 0.8663, and 1.5467, the standard deviation of 0.1996, 0.2585, and 0.0605, and the variance of 0.0398, 0.668, and 0.668. The coefficient of correlation for January and February was found to be +1, indicating a perfect positive correlation between the two months, whereas the correlation for January and March and February and March was found to be zero (0), indicating no correlation between the months.

The amount of Iron (Fe) allowed by the American Public Health (APH) and World Health Organization [14] for drinking water was 0.30 mg/L.

6.4 Nickel (Ni)

The amount of Nickel (Ni) in the five (5) different samples at five different points, as shown in Table 6, decreases at points 1, 2, 3, and 4, while the amount decreases dramatically at point 5.

The amounts at all points (i.e., points 1–5) were less than 0.0100 mg/L in February and March samples. The mean of the three months is 1.0502, 0.0100, and 0.0100, the standard deviation is 0.5094, 0.0112, and the variance is 0.2595, 0.0001, and 0.0001. The coefficient of correlation between the three (3) months was discovered to be zero (0), indicating that there was no correlation between them. WHO has recommends a nickel concentration of 0.02 mg/L for drinking water.

6.5 Zinc (Zn)

The amount of Zinc (Zn) in the five (5) different samples at five different points in mg/kg, as presented in Table 7, for January samples, decreased at points 1 and 2, but increased at points 3 and 4, and decreased at point 5, while increasing at points 1, 2, 3, and 4.

For February samples, the amount decreases from point 1 to point 2, while the amount decreases from point 3 to point 5, and there is a sudden increase in the amount at point 5 that is greater than the amount at points 1, 2, 3, and 4.

For March samples, the amounts at points 1 and 2 increase, but the amount at point 3 decreases to less than that at points 1 and 2, while at point 4, there was a drastic decrease in the amount compared to that at points 1, 2, and 3, but at point 5, there was a drastic increase in the amount that was more than that at points 1, 3, and 4, but less than that at point 2. The mean of the three months is 0.1194, 0.2137, and 0.2596, the standard deviation is 0.0182, 0.0219, and the variance is 0.0003, 0.0005, and 0.0021. The coefficient of correlation between the three (3) months was discovered to be zero (0), indicating that there was no correlation between them.

The heavy metals’ mean concentrations (mg/L) (chromium, iron, nickel, and zinc), and a calibration curve (Figure 1) was plotted using the table to indicate the heavy metals’ concentrations (mg/L) against the metals.

Figure 1.

Comparison between mean samples and WHO maximum concentration limit.

The curve demonstrated an increase in heavy metal concentration (mg/L) in the samples as follows. Iron (Fe) > Zinc (Zn) > Nickel (Ni) > Chromium (Cr). This indicates that iron (Fe) has the highest concentration value in the samples (Figure 2 and Table 8).

Figure 2.

A graph of concentration (mg/L) of heavy metals.

7. Results

Samples/Parameters	pH	Temperature (°C)	Conductivity (μohms/cm)	Turbidity (NTU)
Point 1	7.60	21.30	593.00	28.70
Point 2	6.53	20.80	618.00	14.45
Point 3	7.52	20.80	828.00	43.69
Point 4	6.89	20.20	507.00	103.00
Point 5	6.50	20.90	690.00	14.01

Table 1.

Parameters analyzed for January samples.

Samples/Parameters	pH	Temperature(°C)	Conductivity (μohms/cm)	Turbidity (NTU)
Point 1	6.66	20.30	511.00	26.35
Point 2	6.86	20.80	499.00	18.36
Point 3	6.56	20.50	497.00	23.85
Point 4	6.76	20.40	500.00	25.93
Point 5	6.84	20.70	513.00	31.93

Table 2.

Parameters analyzed for February samples.

Samples/Parameters	pH	Temperature (°C)	Conductivity (μohms/cm)	Turbidity (NTU)
Point 1	6.93	27.60	416.00	49.47
Point 2	7.10	29.30	418.00	42.99
Point 3	7.09	29.80	418.00	36.74
Point 4	7.25	30.10	413.00	41.61
Point 5	7.06	30.00	415.00	39.31

Table 3.

Parameters analyzed for the of March samples.

Samples	January	February	March
Point 1	< 0.0100	< 0.0100	< 0.0100
Point 2	< 0.0100	< 0.0100	< 0.0100
Point 3	< 0.0100	< 0.0100	< 0.0100
Point 4	< 0.0100	< 0.0100	< 0.0100
Point 5	< 0.0100	< 0.0100	< 0.0100

Table 4.

The concentration of chromium (mg/L) in the samples.

Samples	January	February	March
Point 1	0.2354	0.7622	1.6467
Point 2	0.0837	0.5056	1.6454
Point 3	0.9546	0.6152	1.4924
Point 4	0.0357	0.6843	1.3636
Point 5	<0.0100	1.7753	1.5765

Table 5.

The concentration of Iron (mg/L) in the samples.

Samples	January	February	March
Point 1	0.9136	< 0.0100	< 0.0100
Point 2	0.0690	< 0.0100	< 0.0100
Point 3	0.0634	< 0.0100	< 0.0100
Point 4	0.0142	< 0.0100	< 0.0100
Point 5	< 0.0100	< 0.0100	< 0.0100

Table 6.

The concentration of nickel (mg/L) in the samples.

Samples	January	February	March
Point 1	0.0870	0.1933	0.2255
Point 2	0.0900	0.1595	0.3876
Point 3	0.1370	0.2290	0.2116
Point 4	0.1091	0.2087	0.1527
Point 5	0.1741	0.2782	0.3071

Table 7.

The concentration of zinc (mg/L) in the samples.

Metals/Months	January	February	March	Mean	WHO (mg/L)
Zinc (ZN) (mg/L)	0.1194	0.2137	0.2569	0.1967	3
Nickel (NI) (mg/L)	1.0502	<0.0100	<0.0100	0.3567	0.07
Iron (Fe) (mg/L)	0.2587	0.8663	1.5467	0.8906	0.3
Chromium (Cr) (mg/L)	<0.0100	<0.0100	<0.0100	0.0100	0.05

Table 8.

Mean concentration of metals in the samples in comparison with WHO standard.

8. Conclusions

Heavy metals enter the human body through a variety of routes, including drinking water, air, food, and, on rare occasions, dermal exposure. Following absorption, heavy metals are retained and accumulate in the human body. When the research findings are compared to WHO standards, it indicates that the level of contamination in the Romi river with some heavy metal concentrations such as (Iron 0.89 mg/L and Nickel 0.36 mg/L) has exceeded the WHO maximum standard limits (Nickel 0.02 mg/L and 0.030 mg/L). The mean concentrations of the metals: Chromium, Iron, Nickel, and Zinc with the standard deviation was found to be:$<0.01\pm 0.1\mathit{mg}/L$, $0.89\pm 0.1\mathrm{mg}/\mathrm{L}$, $0.06\pm 0.1\mathrm{mg}/\mathrm{L}$, and$0.20\pm 0.1\mathrm{mg}/\mathrm{L}$. This study found that the mean concentrations of chromium and zinc were lower than the World Health Organization’s acceptable limits, while the higher concentration values of nickel were higher$\left(0.06\pm 0.01\mathrm{mg}/\mathrm{kg}\right)$and iron $\left(0.89\pm 0.01\mathrm{mg}/\mathrm{kg}\right)$was discovered to be greater than the WHO standard acceptable limits for heavy metals. This contamination is attributed to the Kaduna Petrochemical and Refining Company’s effluent discharge into the river.