Introduction

Nowadays one in seven people on our planet, lack access to safe drinking water. More than 40 percent of the planet’s population will be living in areas of “severe” water stress and around 768 million people do not have access to a safe, reliable source therefore water pollution has become to a  major global problem and it is leading worldwide cause of deaths and diseases. Pollution of the biosphere with toxic metals has accelerated dramatically since the beginning of the Industrial Revolution [1-3]. Wetland is a water environment which has considerable scientific, economic and social values. They are the habitats of various organisms contributing to the gene cache of microbes, plants and animals on the earth. However, nowadays the pollution and degradation of the wetlands are increasing dramatically [4].  Marine animals can accumulate metals through sea water, suspended particles, sediments and food chains [5]. Permanent contaminants such as metals may be transferred to higher levels in the food chain through environmental expansion. Behavior of trace elements in various weathering environments is dramatically different. In world soil neutral or alkaline weathering environments, U, V, Mo, and Zn have high mobility, while Mn, Pb, Ba, Be, and Bi have low mobility, and Cu, Co, Fe, Ni, Th, Y have very low mobility. Otherwise, in reducing environment conditions As, Ba, Be, Bi, Cd, Co, Cu, Mo, Ni, Pb, Se, Th, U, Zn, V, and Y have a very low degree of mobility [6]. Trivalent chromium occurs widely in nature and is an essentials nutrient required by the human body to promote the action of insulin in body tissues. Chromium as a pure metal has no reported human or environmental toxicity effects. Both acute and chronic toxicity of chromium are mainly caused by hexavalent chromium compounds (Cr VI). Hexavalent chromium is considered the most hazardous of all forms, and in welding fume it is a suspected human carcinogen. DNA damage in welders has been associated with hexavalent chromium exposure [7]. This is consistent with the classification of hexavalent chromium as a human lung carcinogen [8].

Many agricultural by-products such as almond and other fruit or nut shells are available and have low cost. Almond (Rosaceae family) with wide applications in pharmaceutical, oleo chemicals, food and cosmetic industries is considered as a pleasant nut throughout the world. Other than the regular almond, there are more than thirty wild or partially cultivated almond species in the world of which twenty species have been reported in Iran [1, 9]. Iran is the main center for distribution of genus Amygdalus. L .  Amygdalus is one of the most problematic genera in family Rosaceae and taxonomy of this genus like many other genera in this family with numerous problems because of high degree of variation in morphological conditions [10].  (Khatamsaz 1993).It shows high degree of variation within one species, high hybridization inter species and high homoplasy under ecological conditions [11].

As Iran is one of the richest countries in the world as regards genetic resources of medicinal and wild unknown  plants that some of them are export  [12]. We have studied on potential ability of Amygdalus  specie as this endemic specie  found in some parts of Iran especially in south regions due to  accumulate  Chrome and Nickel as the major concern in wetland pollution.

 Materials and Methods

Study of Area

Almond in areas with warm, dry summers and cold winters and short fall grows well. Distribution Almond mountain areas in Zagros foothills of khuzestan begins and in altitudes 600 to 1500 meters above sea level is located (Figure 1). Around the city of Dezful, Izeh, Baghmalek, Masjed Soleiman and Haftgol abundant of almond can be seen [13].  The Izeh fault zone is a transverse fault zone with dextral strike slip (and some reverse component) in the Zagros Mountains (Iran). It causes some structural deformations. This fault zone is acting as eastern boundary of Dezful Embayment and forms subsidence of the embayment [13]. The Type of regional climate is related to the dry forests and minimum temperature of 18.11 °C and the average temperature of 23 °C and the maximum temperature are 48.5 °C.

Shell samples were washed several times with deionized water and dried (sun or mechanical). The adsorbents were then ground in a blender and stored for further use. All reagents and chemicals were used of analytical reagent grade and were obtained from standard sources.

Phosphoric acid, activated carbon, potassium dichromate and other chemicals were obtained from standard sources.

Figure 1: Location of Amygdalus  scoparia  sampling collection. Click here to View figure

Characteristics of waste water

To move forward on chemicals management, a project has been done in Pharmaceutical faculty in Tehran-Iran which has 20 laboratories in chemical and toxicological laboratories whose area of work are divided into two types of educational and research. The research has focused on comprehensive environmental management of the poisonings and exposure to toxic and hazardous chemicals especially Lead, Nickel and Cr (III) and Cr (VI). The waste water of inorganic research laboratory was collected during 2 weeks in summer 2015.

Experimental design and Chemical analysis

The shell part of A. scoparia  was  soaked in phosphoric acid 2% for 24  hours and then dried at 80 ºC in an oven for 24 hours. Dry parts were then ground and weighed. Shell samples (approximately 0.5 g) were digested with concentrated HNO₃ and H₂O₂  [6,7, 25-29 ]. The digested solution was filtered and then analyzed for Pb, Ni and Cr (III) and Cr (VI), concentration using Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES).

Statistical analysis

The values reported here are means of six values. Data were tested at different significant levels using student t-test to measure the variations between the waste water parameters before and after treated by A. scoparia modified shell with waste water. One way analysis of variance (One-ANOVA) was used for data analysis to measure the variations of metal concentrations using SPSS 22.0 software (SPSS Inc, IBM, Chicago, IL).

Results

The mean ±SD values of various physico-chemical and heavy metal characteristics of control (untreated waste water) and treated waste water are presented in Table 1. The results revealed that waste water contained significant quantity of nutrients like Na⁺, K⁺, Ca²⁺, Mg²⁺, TKN, PO₄^3-, SO₄^2- and heavy metals such as Cd, Cr, Cu, Fe, Mn, Pb and Zn. These are very important parameters that lead to water and soil contamination. The values of various waste water characteristics like TDS (2860.00 mg L ^-1), BOD (1450.30 mg L ^-1), COD (3225.00 mg L ^-1), Ca²⁺ (650.90 mg L ^-1), TKN (420.70 mg L ^-1), Cu (10.36 mg L ^-1), Fe (16.84 mg L ^-1), Mn (6.67 mg L ^-1), Pb (9.64 mg L ^-1), Zn (18.66 mg L ^-1), SPC (7.68×10⁸ SPC ml ^-1) and MPN (8.69×10⁵ MPN 100 ml ^-1) were recorded beyond the prescribed BIS standards of irrigation water (Table 1). The higher TDS in the waste water is likely due to the occurrence of feacal matter while the more BOD and COD are associated with the presence of higher biodegradable organic waste in the waste water. The higher number of SPC and MPN in the waste water are the indicator of feacal pollution and pathogens. TKN and PO₄^3- were also recorded higher in the waste water and are associated with eutrophication of aquatic ecosystems. Therefore, various parameters clearly indicated that the waste water was highly rich in plant nutrients, heavy metals and contagious.

Table 1: Physico-chemical and heavy metal characteristics of control (untreated waste water ) and treated waste water by A. scoparisa  shells after 60 hours

Mean ± SD of six values; ^a treated wastewater. Significant -***p>0.1   level: **p>0.01% level; *p>0.05 level; NS-not significant.

Chemical analysis

Experimental results showed that the percentage removal Cr (VI) increases with the increasing amount of adsorbent up to 5.4 g for treated shells by phosphoric acid 2%. After this dose of adsorbent no significant change was observed, but for untreated almond shells percentage removal Cr (VI) increases with the increasing amount of adsorbent.

Metal accumulation in shells increased significantly with an increase in applied metal solution concentration in both lead (figure 2) and Cr (III) and Cr (VI), (Figures 3 and 4  respectively) treated groups. In Figures 2, 3 and 4 the mean contents of heavy metals are reported. The metal concentrations remained high in shells in Cr (III) and Cr (VI), treated groups, while lead metal content was higher in treated shells than untreated shells.  The ratios of shells/water ratios were calculated to indicate the translocation efficiency of Pb and Cr from water to the adsorbents while for the results of nickel translocation was not significant.  The Cr (III) concentrations in samples after 10, 20, 30 and 40 hours  are higher in shells than Cr(VI), hence the translocation factor  ratios were less than one for Cr (VI) treated samples shows that this method is highly suitable for adsorbing Cr(III)  to the Cr (VI). Even though the Cr(VI), concentration of shells  of Cr treated samples in  48 hours  treated samples  is higher compared to controls solutions,  the extent of metal accumulation and uptake efficiency of Cr(III) was lower than that of Cr(VI), in long term contaminated situation study.  Most of shells in Cr (VI) samples deformed after 60 hours remaining in contaminated water. The effect of adsorbent dose on Cr (VI) uptake was investigated by varying the shell adsorbent dose (1, 2, 3, 4 and 6 g 100 ml^-1) for a time interval of 0- 60 hours min (Figure-4).

Figure 2: The mean content of Lead  (mg kg -1)  in A. Scoparia  treatment groups in contaminated  100, 200 and 300 mg kg -1  Lead  solution   in the form of   Pb(NO3 )2 in different pH  and contact times (hours). Click here to View figure

Figure 3: The mean content of Cr(III) (mg kg -1)  in A. scoparia   treatment groups in contaminated  100, 200 and 300 mg kg -1 chrome  solution   in the form of   Cr (NO3 ) 3 in different pH and contact times (hours). Click here to View figure

Figure 4: The mean content of Cr (VI) (mg kg -1) in A. Scoparia treatment groups in contaminated 100, 200 and 300 mg kg -1 Chrome (+6) solution in the form of Cr (NO3 )6  in different pH and contact times (hours) . Click here to View figure

Discussion

The results of present study revealed adsorption capacity of Cr (VI), Cr(III), Pb and Ni  onto  modified almond shells by phosphoric acid  was investigated in a batch system by considering the effects of various parameters like contact time, initial concentrations, pH , temperature, absorbent dose and particle size. The adsorption was pH solution dependent and the maximum adsorption was observed at solution pH of 3.23. Moreover, contents of different heavy metals in the contaminated water showed significant (p <0.05) and positive correlation with contents of Pb (r = +82 to r = +96), Cr⁶⁺ (r = +74 to r = +94), Cr ³⁺ (r = +84 to r = +98), Ni (r = +33 to r = +42) in the wastewater and A. Scoparia  modified shell, respectively. The amounts of Cr (VI) adsorbed increased significantly with increase in dose of A.  scoparia adsorbent (p<0.05)  and their contact time (p<0.05). The results of this study revealed that A. scoparia can accumulate high level of lead, Chrome (VI) and (III)   in a short time and their uptake rate by plant is significantly affected by their concentrations in the contaminated water (p<0.005). A contact time of 48   hours  by almond shell was found to be optimum and 87.1% Cr (VI), 89.8% Cr(III), 84.4% Pb and 48.1% Ni  was removed. Experimental results showed that low cost bio-sorbent was effective for the removal of pollutants from aqueous solution.

According to ATSDR, current evidences indicate that Cr (VI) is a cancer agent only by inhalation. Chronic inhalation studies on mice exposed to airborne Cr (VI) suggest that Cr (VI) is an animal carcinogen [14-15]. The mice developed lung tumors from exposure to 4.3 mg m³ of Cr(VI).However, a number of chronic animal studies showed no carcinogenic effects in rats, rabbits, or guinea pigs exposed to 1.6 mg/m3 of Cr(VI) [14-17]. Thus, cancer effects on animals seem to depend on the type of animal. Eating small amounts of chromium (VI) is not harmful. However, eating or drinking large amounts in food or water can cause an upset stomach, ulcers, convulsions, and damage the kidneys and liver. This type of exposure can be fatal. There is not enough data to know if eating or drinking chromium (VI) causes cancer  [14-17]. The results of this study revealed that A.  scoparia  can accumulate high level of Chrome (VI) and  (III) in a short time and their  uptake rate  by plant  is significantly affected by their concentrations in the contaminated water (p<0.005).

The present investigation shows that the almond shells are effective and inexpensive biosorbents for the removal of Cr (VI) from aqueous solutions. The removal of Cr(VI) from aqueous solutions strongly depends on the contact time, initial concentration, pH, temperature, agitation speed, absorbent dose and particle size. The amounts of Cr (VI) adsorbed increased with an increase in dose of both adsorbents and their contact time. A contact time of 48 hours was found to be optimum. The maximum adsorption capacity was obtained at solution pH of 3.2.

A contact time of 48   hours by almond shell was found to be optimum for Nickel adsorbing and 48.1% Ni was removed.  Although Ni is required in minute quantity for body as it is mostly present in the pancreas and hence plays an important role in the production of insulin. EPA has recommended daily intake of Ni should be less than 1 mg beyond which is toxic [17]. Ni has been identified as a suspected carcinogen and adversely affects lungs and nasal cavities [18].

This research conduct adsorption of heavy metals by agricultural waste and by-product and proved that this friendly method should  gain more attention and research interest for the removal of heavy metals from waste water due to its surface area, adsorption capacity and plenty abundant in nature must be followed seriously.

Also, this research suggests more investigations by other genera and families of cost-effective waste agricultural products applying as adsorbents for these heavy metals and other toxic metals such as cadmium, arsenic and Mercury.

Acknowledgment

Pharmaceutical Sciences Branch, Islamic Azad University (IAUPS) is gratefully acknowledged.

Conflicts of Interest

None of the authors have any conflicts of interest associated with this study.

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