A dried sludge product resulting from the treatment process of domestic wastewater. The exact processes followed for the production of the dried sludge are: Preliminary + secondary treatment of the wastewater stream, thickening, dehydration and drying of the excess sludge.

Endpoint summary

Additional information

Absorption: Based on the UVCB’s substance physicochemical data, it has a low potential of dermal absorption and it is practically non inhalable. Dried sludge is considered practically non inhalable as only a 0,15% has grain size <100μm. Moreover according to acute inhalation toxicity results, no immediate change is provoked in the inhalation track after acute exposure.  Also, dermal absorption is considered as a highly unlikely due to substance’s low solubility and molecular weight. Results from acute dermal toxicity also indicate that the substance is has low skin toxicity.

Metabolism/Excretion: Based on the substance’s basic composition the following metabolic pathways are expected to get involved

 

 Proteins (31%)

Protein metabolism occurs in liver, specifically, the deamination of amino acids, urea formation for removal of ammonia, plasma protein synthesis, and in the interconversions between amino acids. Ingested protein is the sole source of the ten essential amino acids, and the primary source of nitrogen necessary for the synthesis of other amino acids. Protein is digested and broken down to amino acids which are absorbed into the circulation and taken to cells throughout the body, primarily the liver and quickly become combined by peptide linkages. The plasma level of amino acids is tightly controlled and maintained near a constant level. Once the cellular limit of protein storage is met, excess amino acids are degraded and used for energy or stored as fat or glycogen. The liver is the primary site of all amino acid catabolism with the exception of branch-chained amino acid catabolism which occurs in the muscle cells. The urea cycle, in which the toxic compound ammonia is converted to urea, occurs solely in the liver. The synthesis of the plasma proteins albumin, fibrinogen, and globulin also occur in the liver.Plasma proteins such as albumin and coagulation factors constitute approximately 50% of the proteins synthesized in the liver (J. Hampsey, W. Karnsakul, in Encyclopedia of Human Nutrition (Third Edition), 2013)

Proteins are hydrolyzed by a variety of enzymes in cells. Most of the time, the amino acids are recycled into the synthesis of new proteins. If there are excess amino acids, however, or if the body is in a state of starvation, some amino acids will be shunted into the pathways of glucose catabolism (Figure 1). Each amino acid must have its amino group removed prior to entry into these pathways. The amino group is converted into ammonia. In mammals, the liver synthesizes urea from two ammonia molecules and a carbon dioxide molecule. Thus, urea is the principal waste product in mammals produced from the nitrogen originating in amino acids, and it leaves the body in urine.

 

Lipids (7,4%)

Lipid metabolism is involved in different active functions of our body, such as energy storage, hormone regulation, nerve impulse transmission, and fat-soluble nutrient transportation. Lipids serves as an energy source with high caloric density, providing 9 kcal of energy when compared to protein and carbohydrates, which can also store 100,000 kcal of energy in our body functions without any intake of food for 30-40 days, only requiring sufficient water (Ophardt, 2003). Biochemical lipids are stowed in cells all over the body, in specific varieties of connective tissue, named adipose. Lipids protect human organs, such as the spleen, liver, heart, and kidneys, from damage (Church et al., 2012).

Lipids that exist in the blood are absorbed through liver cells and provide the correct concentrations to various parts of the body. The liver plays a key and vital role in lipid metabolism (Ophardt, 2003). The liver serves as a substitute reservoir for storing extensive quantities of excess fat. Through prolonged energy overload, the unspent excess energy is stored in adipose tissue and in hepatocytes in the form of triglycerides (Huang et al., 2011). The metabolism cycle is extended to the citric acid cycle, the urea cycle, and the citric cycle (Arumugam and Natesan, 2017).

Fatty acids are degraded via oxidation, which releases large amounts of ATP and produces sensitive oxygen (Rosca et al., 2012). The glycerolipids biosynthesized through snglycerol-3-phosphate dominate in the liver and adipose tissue (Athenstaedt and Daum, 2006). This review observed various useful metabolic functions of proteins enabling an understanding of metabolic disorders (Huang and Freter, 2015; Trebatická et al., 2017; Musso et al., 2018; Yan and Horng, 2020).

 

Carbohydrates (1,7%)

Carbohydrates are divided into three major groups based on their structures: (1) simple sugars (monosaccharides and disaccharides), such as glucose or sucrose (glucose and fructose); (2) complex carbohydrates, such as glycogen, starch, and cellulose, which are multiple conjugated glucose molecules; and (3) glycoconjugates, which are modified forms of glucose covalently attached to either proteins (glycoproteins) or lipids (glycolipids), which participate in important functions, such as immunity, and as components of cell membranes. This review covers all three groups and highlights their importance in maintaining physiological functions.

Dietary carbohydrates of greatest importance are composed of hexoses such as sucrose (saccharose or table sugar), lactose (milk sugar), galactose (derived from fermented products) and maltose (derived from hydrolysis of starch) and also pentoses such as xylose and arabinose (from fruits). Food digestion starts in the mouth through secretion of salivary alpha-amylase (or ptyalin) that hydrolyses alpha-1,4 (α-1,4) linkage of starch (or amylum) and converts it to maltose. The next enzyme is pancreatic-amylase (or amylopsin) in the small intestine that digests 60% of starches. Intestinal epithelial cell enzymes degrade 6-carbon (6C-) carbohydrates. These enzymes are lactase for degradation of lactose to glucose and galactose,sucrase for degradation of sucrose to its constituent components (glucose and fructose) and maltase for degradation of maltose to two glucose molecules. The 5C-carbohydrates such as xylulose, arabinose, ribose and ribulose easily diffuse into the intestinal ab sorptive cells and do not need degradation.

Absorption of the 6C-carbohydrates from intestinal epithelium happens in two ways: passive and active transport systems. In the passive diffusion form, phosphorylation of carbohydrate (e.g., glucose or galactose) in the intestinal cells leads to their facilitated transfer to the circulation. Glucose-6-phosphate (G6P) and galactose-6- phosphate (Gal6P) are then dephosphorylated and enter the liver. In the active diffusion form, carbohydrates utilizing a mobile carrier protein coupled with the sodium/potassium (Na + /K + ) pump  nd against the gradient together with Na + ion enter enterocytes . Therefore, the Na + /K + pump using ATP as its source of energy exchanges 3 Na + ions with 3 K + ions. Galactose and fructose are converted to glucose in the liver. Glucose is used in different metabolic pathways for (i) stability of blood sugar in the hypoglycemic state, (ii) energy supplier of the peripheral tissues, (iii) energy storage in the liver and skeletal muscle in the form of glycogen to be used in exercise , (iv) energy storage in the adipose tissue following conversion to triglycerides (TG, TAG, triacylglycerol or triacylglyceride)  in the case of excess glucose and (v) stability of body temperature (M. Dashty / Clinical Biochemistry 46 (2013) 1339–1352Monireh Dashty) .

Moreover based on the results from the bacteria mutation test and the biodegradation test, enzymatic activation does not increases its biological interaction potential  and it has no bioaccumulation properties.