Chromium from tannery waste in poultry feed: A potential cradle to transport human food chain

Raw skin trimmings (RST), wet blue shaving dusts (WSD), and lowchrome wet-blue scraps (LCWS) are protein-rich tannery wastes which are used as one of the main ingredients for manufacturing of poultry feeds. These feeds may contain toxic chromium, which accumulates in the poultry and cause chrome contamination in human food chain. It is a major concern for humans consuming these poultry as part of their regular diet. In this study, tannery wastes, 12 brands of poultry feeds, broiler chickens (Gallus gallusdomesticus) nourished on chrome containing feed were collected for the investigation of total chromium present and circulated through the process of ingestion and digestion. The chromium content of RST and all poultry feed samples were found to be below 0.03 mg/kg, except the samples of WSD, LCWS, starter feed (FS10), and grower feed (FS11), which were 29854.4 ± 0.9, 14902.0 ± 1.01, 618.3 ± 0.9 and 3.02 ± 0.07 mg/kg, respectively. The chromium in protein concentrate made from WSD and LCWS were 21535.4 ± 1.01 and 13421.8 ± 0.04 mg/kg, respectively. Various body parts of chickens were found to be contained the element in the range of 0.42 to 0.84 mg/kg. Hence, there is a potential human health risk through consumption of contaminated poultry meat as it exceeded the daily adequate intakes (AIs) level. *Corresponding author: Sobur Ahmed, Institute of Leather Engineering and Technology, University of Dhaka, Dhaka 1209, Bangladesh E-mail: soburahmed@du.ac.bd Reviewing editor: Fares Almomani, Qatar University, Qatar Additional information is available at the end of the article

ABOUT THE AUTHORS Sobur Ahmed, Fatema-Tuj Zohra, and Md. Shiblee Hider Khan belong to the same working group at the Institute of Leather Engineering and Technology, University of Dhaka, Bangladesh. Their research interests are in the domain area of leather science with waste management and pollution control. Ahmed has published a book and 15 research papers in the national and international reputed journals. Fatema has published a book and 10 research papers in the national and international journals.
Md. Abul Hashem is an assistant professor in the Department of Leather Engineering at Khulna University of Engineering and Technology, Bangladesh with research interest in the leather engineering and waste management. He published 22 research articles in different national and international journals PUBLIC INTEREST STATEMENT Bangladesh is a densely populated developing country where poultry is one of the main cheap sources of protein as human diet. A few farms reared poultry using feed made from tannery solid waste. About 80% protein-rich solid wastes generated from tannery during leather processing and 90% of these leather processed by chrome tanning method. Chromium was detected in the collected poultry feeds made from wet blue scraps and saving dusts. The chromium content was found to be accumulated in the body parts of chickens reared with the chrome-containing poultry feed. Trace amounts of chromium (III) is essential for certain metabolic functions in the human body. However, excessive heavy metals may cause serious adverse effects on human health. Chromium did not found in the poultry feed prepared from raw skin trimmings. Hence, the consumption of poultry meat reared by these feeds may not be exposed to health hazards.
Solid wastes generated in tannery industries mainly consist of skin trimmings, keratin wastes, fleshing wastes, chrome shaving wastes, and buffing wastes (Kanagaraj, Velappan, Babu, & Sadullah, 2006). Chrome shaving dusts, wet blue scraps, and buffing dusts contain huge amount of chromium. It is reported that chrome shaving dusts contain chromium in the range of 10.68 ± 1.98 mg/g (Swarnalatha, Srinivasulu, Srimurali, & Sekaran, 2008). Disposing of this high chromium content solid wastes as land fill or dumping these may cause leaching of chromium to groundwater and thus cause its entry into the human food chain. In Bangladesh, every year 5.9 × 10 4 tons of hides and skins (bovine, sheep, lamb, goat, and kid) are used are raw material for leather production (Food and Agriculture Organization of the United Nations [FAO], 2013), leading to huge amounts of solid wastes being generated by the tanneries. Injudicious disposal of solid wastes from the tanneries cause environmental pollution, which ultimately has detrimental effects on human health when exposed it through various agencies (Sundar, Raghavarao, Muralidharan, & Mandal, 2011). Due to the generation of solid, liquid, and gaseous pollutants, Department of Environment (DoE), Bangladesh has categorized tanneries as a 'red' category industry. Many research groups have already investigated different ways to manage the solid wastes originating from the tanneries (Cabeza et al., 1998;Ravindran & Sekaran, 2010;Shanmugam & Horan, 2009).
In Bangladesh, several large and many small mills are converting the solid wastes into protein concentrates without following any appropriate standard operating procedure. This protein concentrate is mixed with other ingredients to prepare poultry feeds. Each large mill produces 200-250 tons of protein concentrate per day (Hossain et al., 2007). Transfer of chromium into poultry may occur through these feeds, which then enters into the human food chain. It is very important to know the quantity of chromium present in the feed and the amount of chromium transmitted to the body parts of chicken which are consumed as human food.
In this study, an investigation was carried out to determine and quantify the chromium content in (1) solid wastes used in producing protein concentrate, (2) prepared poultry feed, and (3) different body parts of chicken which were reared by selected feed.

Sampling
Raw skin trimmings, chrome shaving dusts, and wet blue scraps were collected from Hazaribagh tannery area, Dhaka in a uncontaminated polyethylene bags. Poultry feed samples for broiler chickens (Gallus gallusdomesticus) were collected from a poultry farm of Dhaka city and marked as: (a) starter feed, (b) grower feed, and (c) finisher feed. Two chickens reared on the feeds containing chrome were collected from the same poultry farm. The legs of both the chickens were cleaned with deionized water and wiped with non-adhesive tissue paper. The chickens were weighed after proper drying and denoted as A (1.5 kg) and B (1.3 kg). The chickens were slaughtered with sharp stainless steel knife by slitting the throat.

Sample preparation
The slaughtered chickens were hung upside down for 30 min to allow all the blood to be drained. Then every part of the chickens, i.e. meat, liver, heart, gizzard, and bones were separated with stainless steel knife; each part was washed with deionized water and air-dried on Petri dishes. All glassware and stainless steel knife were sterilized at oven for 72 h at 125-130°C. Then, samples were cut into small pieces with stainless steel knife and each type was mixed homogenously. Clean and hygienic conditions were maintained at all times to prevent contamination.

Reagents
All stock solutions were prepared from analytical grade reagent. The chrome shaving dusts and wet blue scraps were digested with nitric acid (Merck, India), hydrochloric acid (Merck, India), and sulfuric acid (Merck, India). The feed samples were digested with nitric acid and perchloric acid (BDH, England). Freshly prepared double deionized water was used in all the experiments. Prepared samples were kept in acid-washed plastic polymer bottles.

Acid digestion
Different methods were used for preparation of different types of samples. All the samples were conditioned following standard IUC method before analysis.

Acid digestion of raw skin trimmings, shaving dusts, and wet blue scraps
For preparing the raw skin trimmings, shaving dusts, and wet blue scraps, about 50 mg of samples were poured into the digestion vessel and 3 mL of nitric acid (HNO 3 ) was added, in which 1 mL of hydrochloric acid (HCl) and 3 mL of sulfuric acid (H 2 SO 4 ) was added. The mixture was gently swirled manually for 10 min before the vessel was stoppered. Then it was digested with microwave digester at 190°C and 35 bar pressure for 20 min. The obtained solution was cooled, filtered, and diluted to 25 mL (Huq & Didar-Ul-Alam, 2005).

Acid digestion of poultry feed
About 0.4 g of the feed sample was taken and 5 mL of nitric acid (HNO 3 ) was added to it. The mixture was left standing for 1 h. After 1 h, 3 mL of perchloric acid (HClO 4 ) was added to the sample and it was left standing for 30 min. After 30 min, the sample was digested at 200°C on a hot plate. The digested sample was diluted to 25 mL and filtered through Whatman 44 filter paper (Hossain, Barreto, & Silva, 1998).

Acid digestion of organ
The biological samples (body parts of chicken) were washed with distilled water and then air dried. They were conditioned for 72 h at 60°C to remove the moisture. The samples were then cut into small pieces and each type was mixed homogeneously. About 0.4 g of these samples was taken in a beaker and left for 1 h after 5 mL of nitric acid (HNO 3 ) being added to it. Then, 3 mL of perchloric acid (HClO 4 ) was added to it and left for 30 min. After 30 min the sample was digested at 200°C on a hot plate. The solution obtained was diluted to 25 mL and filtered with Whatman 44 filter paper (Hossain et al., 1998).

Determination of chromium
Acid digested aliquot was analyzed with the use of atomic absorption spectroscopy (SHIMADZU, AA-7000) in order to quantify the chromium content. Direct flame (air-acetylene) at the wavelength of 357.9 nm was employed at this stage of the procedure. The detection limit of the atomic absorption spectroscopy for chromium was 0.03 mg/kg. The machine was calibrated and ISO 17025 certified.

Chromium content in tannery waste and protein concentrate
The chromium concentration in the tannery waste and protein concentrate is shown in Table 1. It is clear from the data that out of the three raw materials, two contained high amounts of chromium. The chromium content in the wet blue shaving dust (WSD) was 29,854.4 ± 0.9 mg/kg and in the lowchrome wet blue scraps (LCWS) was 14,902.0 ± 1.01 mg/kg. In the raw skin trimmings, chromium content was below 0.03 mg/kg. The chromium content in the 12 different poultry feeds is shown in Table 2. Out of 12 poultry feeds tested, only 2 contained chromium. The chromium content in the samples FS10 (starter feed) and FS11 (finisher feed) were 618.3 ± 0.9 and 3.02 ± 0.07 mg/kg, respectively. The chromium content in the remaining 10 feed samples was less than 0.03 mg/kg.

Chromium content in the body parts of chicken
Standard poultry feeds in Bangladesh are made by adding various ingredients, e.g. maize, wheat, soya oil cake, barley, and ground rice with protein concentrate. It was observed that in the poultry farm used for sampling, three types of feed were used to rear the chickens. The transport mechanism of chromium from tannery waste to human food chain through poultry feed is shown in Figure 1.  It is clear from Figure 2 that the chromium accumulated in the different body parts, i.e. meat, bone, heart, gizzard, and liver of the chickens reared with chrome-containing poultry feed samples FS10 and FS11. The chromium content in the heart and gizzard of chicken B (wt. 1.3 kg) was much lower than that of chicken A (wt. 1.5 kg), whereas it was higher in the bone of chicken B. The highest amount of chromium was found in the heart of chicken A, i.e. 0.84 mg/kg. Table 3 shows the adequate intakes (AIs) of chromium required or acceptable for humans, from infant to above 50 years. It is evident that a minuscule amount of chromium is required for humans of the all ages. In case of infants, per day requirement of chromium is 0.2 μg; whereas, for children (8 years), it is 75 times higher than that of infants. In addition, for the average male aged of 9-50,