Investigation of contamination pathway and human health risk assessment from metals in milk from the cows grazing in an industrial area: a mass balance approach


 The water bodies within the industrial areas are often used for the disposal of effluents leading to heavy metal contamination in water, soil, and vegetation. However, the impact of this metal enrichment on the food web has not been much explored. The present study investigates the food chain contamination of eight metals (Al, Cd, Cr, Cu, Fe, Mn, Pb, and Zn) in the milk from the cattle grazing on a shallow lake bed within the industrial town of Ranipet, India, and associated health risk from the consumption in adults and children. The average concentrations were found to be 24.93, 7.08, 3.31, 0.18, 0.12, 0.08, 0.014, and 0.008 in mg/L for Zn, Al, Fe, Cr, Pb, Mn, Cu, and Cd, respectively. The hazard indices ranged from 0.55 to 1.85 for children; the Incremental Lifetime Cancer Risk (ILCR) values of Cd and Cr were above 10 − 4 for consumption of milk in both adults and children, which signify serious health risk. The mass balance evaluates the primary intake of all the metals, except Al, are from forage; where for Al it is from the soil. The existing milk consumption patterns projected that 531 children and 1279 adults, drinking contaminated milk are at considerable risk. The analyses of tail switch hair samples indicated the cattle are also environmentally exposed to metals indicating their subclinical effect. Hence the study alerts the elevated and often overlooked risk associated with the food chain contamination from milk in the industrial belt and recommends stringent quality control and monitoring.


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The milk and its products are basic foods with essential source of nutrients in daily human diet, especially 90 infants. Among them the cow milk is considered as one of the greatest nutritional valued food as being vital in 91 children's diet (Castro Gonzalez et al. 2017). So, the metal content in the milk can be a significant indicator of 92 food hygiene as well as degree of contamination (Licata et al. 2012). Further, the children are more vulnerable 93 than adults to acute toxicity at lower doses as their defence mechanisms aren't completely developed. Due to their 94 undergoing developmental processes, the acute or chronic exposures can lead to serious anomalies which can 95 either persist or develop at later age (Scheuplein et al. 2002). Hence the contamination of cattle milk is a matter 96 of increasing concern and need to be addressed without any tolerance.

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The metal contamination of milk has been reported earlier in many parts of the world; especially due to 99 anthropogenic activities (Castro Gonzalez

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Soil was considered as sink of metals and the exact anthropogenic metal contribution was due to 113 discharge of industrial effluents. The ruminants grazing in the industrially influenced areas has different sources 114 for metal intakes such as contaminated water, forage and soil (Zhou et al. 2019;Iqbal et al. 2020). The soil 115 ingestion while grazing was out looked by most of the studies as they often consider milk contamination and 116 associated health risks; which need to be explored. Also, the quantified contribution of metals from the different 117 intake sources to the milk is not apprehended properly. Hence, for the detailed understanding, mass balance needs 118 to be evaluated. This aids to distinguish the appropriate sources of metals to the cattle and in identification of 119 intake and output route of metals which helps to formulate mitigation strategies. For the best of the knowledge, 120 the mass balance concept for the milk contaminated by the metal including soil as potential intake has not been 121 studied before.

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Ranipet is an industrial hub in southern India mainly known for its leather production, contributing 37%   The present study was conducted to identify the metal contamination transfer from forage, soil and water to the 155 cattle reared in Puliyanthangal Lake. Also, the transfer of metals through food chain by consumption of milk by 156 adults and children was evaluated. Hence a systematic procedure was adopted in selection of various types of 157 samples. The methodology adopted is shown in the Fig. 2.

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All the samples were collected during the month of April, 2018. Ten healthy cows among the cattle 159 reared in the study area were randomly selected to maintain uniformity in sampling and their respective milk, 160 urine and dung were collected. All the samples were collected with the consent of the owners to use in this study.

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The cattle were never stimulated or forced to excrete dung and urine.

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The water samples (n=7; W-1 to W-7) were collected from different corners of the lake without 163 disturbing the sediments in pre-washed sterile plastic containers and they were transferred to laboratory in icebox. 7 Then they were filtered through Millipore 0.45µm filter paper; acidified to pH less than 2 and stored in refrigerator 165 until analysis at 4⁰ C (Miclean et al. 2019).

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The lake area is predominated by Cynodon dactylon (Bermuda grass) and limited amount of Sida acuta 167 (common wireweed) and Eclipta prostrata (false daisy). All three types of plants are being consumed by the cattle 168 were considered in this study. As per the area preliminary investigation, the daily weighted consumption by cattle 169 was considered as 80:10:10 for Cynodon dactylon, Sida acuta, and Eclipta prostrata respectively. The plant 170 samples (n=7; P-1 to P-7) were collected along with their root from the accessible parts of lake area where cattle          Puliyanthangal Lake. Total number of cattle which are grazing regularly in the study area were counted as ninety-325 one from thirty-eight owners. The self-consumption of milk by these thirty-eight families was calculated and 326 averaged. Apart from this, the total milk yield from the ninety-one cattle were estimated to be 339 L per day with 327 an average yield of 3.72 L of milk per day per cow.

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The results from the survey showed that, the average daily consumption of milk per family was around 329 0.56 L (

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Market survey was conducted to understand the dietary habits and consumption patterns among the local 336 consumers of this milk from ten families ( Table 3) The survey was conducted among the cattle herds and owners to identify the average daily intake of feed and 343 water of cattle along with their average daily milk yield. Also, the data regarding average daily excrements of 344 urine and dung were collected. The intake of forage by cattle was in the range of 20 -30 kg/day whereas the 345 water intake was 30 -40 L in a day (Table 4). The yield of milk from a single one ranged from 2 -6 L per day.

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Also, the daily excrements from cattle in the form of urine and dung were 5 -8 L per day and 6 -10 kg per day 347 respectively. Hence, for the mass balance study, the mean of these values collected from ten cattle were utilized.

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To investigate the primary source and sink of metals in the cattle, mass balance study was conducted by calculating 350 total metal intakes and outputs. The difference between the input and output provides insights about the 351 14 accumulation patterns of different metals into the cattle. Also, the cattle ingest soil due to grazing of root crops to 352 ground level. Hence, ingestion of soil while grazing was considered as one of the input of metals to the cattle. The 353 soil ingestion rate was estimated to be in the range of 0.1 to 1.5 kg/animal per day; with a median value of 0.5 354 kg/animal per day. Hence, this value was adopted for calculating soil ingestion rate of cattle per day in the mass 355 balance study (Healy 1972;Mayland et al. 1975). Also, the mean metal concentrations of soil from the study area     Table S2). This indicate 446 that the cattle are severely exposed to metal toxicity. Apart from that the human health risk associated 447 with the consumption of cattle meat also needs to be evaluated.  Table 1 Mean metal concentrations in Lake water, forage, soil, cow milk, cow urine and cow-dung samples 575 (water, milk and urine values are in mg/L whereas forage and dung values are in mg/kg) 576 Table 2 Survey results of estimation of total milk yield and self-consumption patterns from cattle owners 577 Table 3 Market survey results of estimation of daily milk intake in child and adult from consumers 578 Table 4 Survey results of estimation of average daily intakes, excretions and milk yield of cattle from cow herds 579 and owners 580 Table 5 Chronic daily intake (CDI) of metals by consumption of milk from study area 581 Table 6 Hazard quotient (HQ) of metals by consumption of milk from study area 582 Table 7 Principal component analysis loadings for the metals in the milk samples