Heavy metal toxicity is a major form of environmental pollution. Their tendency for bio-accumulation and bio-magnification in the food chain affects human health. An investigation was carried out in North-24-Parganas of West Bengal. Soil, water and chevon samples were collected from targeted areas over a span of six months and were analyzed for the presence of lead, arsenic, iron and zinc applying atomic absorption spectrophotometry. Soil samples revealed high concentration of iron and zinc whereas water samples indicated high concentration of iron and arsenic. These levels did not impact the overall edible quality of meat because concentration of lead and arsenic were below detection limits and concentration of iron and zinc were mostly below maximum permissible limit. Thus advocating, chevon quality from goats reared in areas having high heavy metal residual content is largely within acceptable limits, however continuing elevation of levels may cause reverse impact in future.
Environmental pollution is a major global problem posing serious risk to animals as well as humans. There is an increasing concern about environmental pollutants being emanated into livestock production system (Rajaganpathy, 2006). Heavy metals from manmade pollution sources are continuously released in the aquatic and terrestrial eco-system. Heavy metals like lead and arsenic are significant environmental pollutants. Elements like iron and zinc are essential in small quantities but when exceeding a specific concentration, they tend to become toxic (Peralta-Videa et al., 2009). Other major pathway for soil and water pollution is through atmospheric deposition of heavy metals from point sources (viz. metalliferous mining, smelting and industrial activities) and non-point sources of contamination (viz. fertilizers, pesticides, sewage sludge, organic manure and compost) (Singh, 2001). Additionally, foliar uptake of atmospheric heavy metals from emission gas and absorption from soil as well as surface deposits has been identified as an important pathway of heavy metal contamination in vegetable crops (Kaur, 2006). Contamination with heavy metals is a serious threat because of their toxicity, bio-accumulation and bio-magnification in the food chain (Demirezen et al., 2006).
High levels of heavy metal residues in the soil and water of West Bengal have been a matter of concern (Chakraborti et al., 2001). Gupta et al. (2008) has reported significant levels of arsenic residues in vegetables grown on waste water. Such contaminated agricultural products may lead to chronic toxicity in human beings (Roy Chowdhury, 2002). Farm animals are also an important indicator for environmental pollution (Kottferova et al., 1995). Exposure of farm animals to heavy metals is a major public health concern because these animals are reared for milk and meat (Inam et al., 2000) and consumption of such polluted food can have direct physiological and toxicological effect on human health. The role of livestock for income generation, food supply and financial security for the rural population is well documented (Tanusha et al., 2019). Goat rearing is a counterpart of mixed farming systems. Grazing on contaminated soil has resulted in higher levels of toxic metals in raw meat (Sabir et al., 2003) as well as meat products (Gonzalez-Weller et al., 2006).This study was proposed to ascertain the concentration arsenic, lead, iron and zinc in the soil, water and meat of goats reared in North-24 Parganas, thus establishing a relationship between the concentration of heavy metals in the environment and determining the safety of goat meat for human consumption.
Materials and Methods
The investigation was carried out in Barrackpore (22.76°N 88.37°E), Barasat (22.72°N 88.48°E) and Bashirhat (2°39′26″N 88°53′39″E) of North- 24 Parganas, West Bengal, India for a period of six months. Composite samples of soil were collected from a depth of 15 cms, dried at 105+5˚C, ground, sieved through a 2 mm mesh and stored in sterile polyethylene bottles until further analysis. Water used to irrigate plants and feed animals were collected, preserved and analyzed as per APHA (1995) guidelines. Castrated Black Bengal goats of 40 weeks age, were purchased locally from the marginal farmers rearing them. They were fasted overnight with free access to water, slaughtered. From each carcass meat from leg, loin and shoulder were collected, vacuum packed and frozen at -20˚C until further analysis.
All samples were digested by tri-acid (Datta et al., 2010). The digest was slowly evaporated to near dryness, cooled and dissolved in 2.0% HNO3. It was then filtered through Whatman Filter Paper no. 42 and diluted to a volume of 50 ml with 2.0% HNO3. This solution was then analyzed by atomic absorption spectrophotometer (GBC,932 Plus- AAS, Australia) in flame mode using air-acetylene flame for lead, iron and zinc and graphite hydride mode for arsenic, using air-acetylene flame for arsenic. The absorption of these elements was compared to standard absorption and the residue levels were expressed as ppm for Pb, Fe and Zn and ppb for As.
Total number of samples analyzed were 180 (five samples each for soil, water, shoulder muscle, thigh muscle and loin muscles, for each month; here n=30). For each table, the data are expressed in parts per million (ppm); parts per billion (ppb) and below detection limit (BDL), wherever applicable. Each S. No. refers to the consecutive months of samples collected in the 6 months period. All the data obtained were analyzed statistically to draw valid conclusion in SPSS (version 16.0) software. Data related to the effect of different wholesale cut were analyzed by one-way ANOVA according to Duncan’s multiple range test (Duncan, 1955). The results were expressed in terms of mean and standard error (SE) of mean. A probability value of p<0.05 was described as significant and p<0.01 was noted highly significant.
Results and Discussion
The data pertaining to As content in different samples are presented in Table 1. Arsenic content in the soil of Barrackpore, Barasat and Bashirhat ranged from 4.063-8.688 ppm, 4.85-5.48 ppm and 4.64-5.44 ppm, respectively. All values were within acceptable limits and in accordance to the observations made by Roy Chowdhury et al. (2002). It was noted that the concentration of arsenic in surface water of Barasat and Bashirhat ranged from 0.319-0.488 ppm and 0.0291-0.482 ppm, respectively. These values were in coherence to that observations made by Bera et al. (2010) and Chakraborti et al. (1998). Water samples from Barrackpore showed 4.413 – 8.141 ppm of As. The BIS (1991) standards allow a maximum of 0.05 ppm of As in drinking water. Exhibiting that most of the values recorded for water samples of barrackpore exceeded safety limit. The residual concentration of arsenic in the shoulder, thigh and loin muscles of goats reared in all three areas were BDL.
The data representing the Pb content in different samples are presented in Table 2. Lead content in the soil of Barrackpore, Barasat and Bashirhat ranged from 2.67-9.45 ppm, 7.56-11.8 ppm and 7.4-12.9 ppm, respectively. All values were within acceptable limits, as mentioned by Roy Chowdhury et al. (2002). The concentration of lead for water samples of Barrackpore were BDL whereas for Barasat and Bashirhat it ranged from 0.001-0.009 ppm and 0.002-0.015 ppm, respectively. As per BIS (1991), these values were within maximum permissible limit and were in coherence with the findings of Kar et al. (2008). The lead concentration recorded for all the chevon samples were BDL.
Table 1: Residual concentration of arsenic
|Parameter||Soil (ppm)||Water (ppm)||Chevon(ppb)||Soil (ppm)||Water (ppm)||Chevon(ppb)||Soil (ppm)||Water (ppm)||Chevon(ppb)|
S- shoulder, T- thigh, L- Loin
Table 2: Residual concentration of lead
S- shoulder, T- thigh, L- Loin
These findings were contrary to those made by Robinson (1994) who reported lead concentration to the extent of 29 ppm in goat meat from Chennai city.
The observations related to the Fe content in different samples are presented in Table 3. Iron content in soil of Barasat and Bashirhat ranged from 6210-6921 ppm and 5428-8210 ppm, respectively. Both these values were considered to be with in normal range and in accordance with the findings of Roy chowdhury et al. (2002). On the contrary, concentration of Iron in the soil of Barrackpore ranged from 11907-19997 ppm, much higher than normalcy. Surface water of Barrackpore, Barasat and Bashirhat contained Iron in the concentration of 1.031-6.0551 ppm, 0.651-1.744 ppm and 0.653-2.635 ppm, respectively. These observations were in coherence to the findings of Kar et al. (2008) but exceeded the BIS (1991) standard which allows a maximum of 0.3ppm of iron in drinking water. The muscle samples exhibited iron content in the different wholesale cuts of chevon for Barrackpore, Barasat and Bashirhat ranged from 14.964-30.069 ppm, 15.601-32.635 ppm and 10.383-32.380 ppm, respectively. All the values were below the maximum permissible limit of 3000-5000 ppm for muscle foods. These findings in meat were in coherence to the findings made by Iwegbue et al. (2008).
The data reporting the Zn content in different samples are presented in Table 4. Zinc content in the soil of Barasat and Bashirhat ranged from 38.2-49.5 ppm and 34.5-52.8 ppm, respectively which according to Roy Chowdhury et al. (2002) was considered to be normal. The zinc concentration for soil of Barrackpore was 380.5-1141.2 ppm, a value much higher than normalcy. Zinc concentration in surface water of Barrrackpore, Barasat and Bashirhat ranged from 0.0572-0.299 ppm, 0.053-0.095 ppm, and 0.007-0.111 ppm, respectively. All these values were in coherence to the findings of Kar et al. (2008) but exceeded the BIS (1991) standards. Zinc concentration in meat samples ranged from 14.865 to 54.305 ppm, most of the values were below maximum permissible limit except a few samples obtained from Barrackpore area which pertained to p >0.05, hence considered as non-significant. Similar studies conducted by Coleman et al. (1992) and Jayasekara et al. (1992) reported fresh meat samples having zinc below 50 ppm, on the contrary a study conducted by Langsland et al. (1987) showed zinc level of 57 ppm in sheep muscle. Gonzalez-Weller et al. (2006), Robinson (1994), Abu Donia (2008) and Coleman et al. (1992) have established the presence of heavy metal residue in meat and meat products.
Table 3: Residual concentration of iron
|1||16447.32+0.803||1.031+ 0.482||25.947+0.253||17.168+0.199||21.105 + 0.172||6740 + 0.829||1.234+ 0.569||22.185+
|19.331+ 0.191||6840+ 0.524||1.589 +0.576||14.061 +0.199||26.354+ 0.172||21.652 0.132|
|2||11907+ 0.543||2.402+ 0.624||19.177+0.172||21.957+0.149||20.956+0.168||6524+
|15.601+ 0.157||6651+ 0.625||0.653+ 0.479||10.838+0.149||24.568+ 0.206||22.852+ 0.125|
|3||13860+ 0.495||6.0551+0.579||22.725+0.206||24.701+0.144||15.839+0.178||6648+ 0.648||2.345+
|24.080+ 0.165||7351+ 0.798||1.584+ 0.612||19.185+0.144||22.654+ 0.268||19.648 +0.174|
|4||19997+ 0.85||1.255+ 0.6||30.069+0.268||16.998+0.218||14.964+0.172||6210+ 0.687||0.651+
|26.165+ 0.222||18.336+ 0.371||5428+ 0.813||1.413+ 0.611||18.651+0.132||23.581+ 0.194||20.484+ 0.118|
|5||17567+ 0.548||1.999+ 0.473||21.392+0.19||24.515+0.184||19.479+0.215||6320+ 0.521||1.234+
|21.851+ 0.199||30.383+ 0.271||6591+ 0.685||2.635+ 0.493||19.74+ 0.218||25.168+ 0.186||21.428+ 0.135|
|6||18269+ 0.801||4.512+ 0.527||24.568+0.16||22.458+0.187||18.632+0.16||6921+ 0.801||1.413+
|20.628+ 0.417||22.654+ 0.169||8210+ 0.169||1.365+ 0.463||15.242+0.235||24.694+ 0.187||23.58+ 0.18|
S- shoulder, T- thigh, L- Loin
Table 4: Residual concentration of zinc
|49.22+ 0.28||45.145+0.303||45.69+ 0.161||51.5+ 0.254||0.058+ 0.102||15.31 + 0.107||43.851+0.268||24.735+ 0.116|
|2||457.5+ 0.251||0.0896+0.154||38.235+0.147||22.080+0.302||15.505+0.209||48.2 + 0.299||0.084+ 0.157||54.305+ 0.213||33.765+0.325||24.73+ 0.18||38.2 + 0.283||0.111+ 0.154||14.99+ 0.102||46.328+0.361||29.689+ 0.134|
|3||380.5+ 0.282||0.118 + 0.214||42.790+0.163||22.315+0.215||39.325+0.245||42.6+ 0.259||0.095+ 0.214||44.37+ 0.293||47.625+0.275||28.765+ 0.169||34.5+ 0.362||0.064+ 0.104||18.642+ 0.108||36.891 + 0.216||27.168+ 0.12|
|4||860.5+ 0.362||0.299 + 0.451||42.540+0.125||25.565+0.268||14.865+ 0.217||40.6+ 0.282||0.083+ 0.452||48.905+ 0.189||29.89 + 0.296||37.425 +0.174||48.9+ 0.252||0.036+ 0.151||17.832+ 0.108||39.548 + 0.246||35.284+ 0.13|
|5||1141+ 0.254||0.291+ 0.441||42.275+0.158||30.825+0.267||19.115+0.278||49.5+ 0.363||0.053+ 0.441||50.015+ 0.175||27.415+0.30817||26.405 +0.234||52.8+ 0.297||0.007+ 0.211||22.546+ 1.029||37.258 + 0.223||32.546 + 0.2|
|6||785.2+ 0.364||0.254+ 0.325||44.528+0.168||28065+0.272||28.352+0.229||38.2+ 0.254||0.082+ 0.036||47.895+ 0.168||35.681+0.287||27.389 +0.176||36.4+ 0.283||0.095+ 0.216||24.682+ 0.015||44.581 + 0.261||38.642+ 0.211|
S- shoulder, T- thigh, L- Loin
On the contrary studies conducted by Nkansah et al. (2014) revealed presence of both Pb and As in chevon samples but the values were below maximum permissible limits, similarly Rooke et al. (2010) and De Smet et al. (2016) established that the response in muscle to increased dietary concentrations of zinc and iron is mostly absent. Rudy (2009) stated that mutton obtained from sheep upto the age of 8 months (approximately 40 weeks) raised in a polluted environment has Pb and As content at Below Detection Limit. All these outcomes reasoned the outcomes of this investigation.
Chevon obtained from goats up to 40 weeks age group, is safe for consumption even if procured from areas having high heavy metal concentration either in soil or water or both. However, continuing elevated levels may cause reverse impact in future.
We are grateful to the Director of Central Inland Fisheries Research Institute (ICAR), Barrackpore, Kolkata, India for providing the opportunity to conduct experiments and analyze data at their facility.