Concentrates of lead and zinc compounds with sulfur resulting from hydrometallurgy (hot acid leaching, super-hot acid leaching and flotation)

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Study well documented, meets generally accepted scientific principles, acceptable for assessment.Read-across justification: Read-across from the most critical and bioavailable constituents (lead and its compounds):Based on the mineralogical composition, lead is the main constituent in the target substance and appears in sulphate form. The target substance is a solid inorganic UVCB substance and insoluble in water. Therefore, the transformation/dissolution study (OECD guidance 29) was conducted for the target substance to focus on the most critical bioavailable constituents of the substance. According to the T/D study results, the readily soluble constituent is lead. Based on the hazard profile of lead it is also the most hazardous constituent of this substance. Therefore, and in order to avoid the unnecessary animal testing, the read-across data from the most critical constituent is used to evaluate the short-term and long-term toxicological adverse effects of the target substance. The read-across data focuses on the properties of lead sulphate and other bioavailable forms of lead.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

1978

Materials and methods

Objective of study:

other: absorption and excretion

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

(1) Rats (8 animals per group) were given 1 uCi of 203Pb and various amounts of lead chloride (1 ng to 1 mg) by oral gavage. Four hours later, the intestinal tract was removed and whole body radioactivity was measured and compared to similar measurements in the live animal prior to test dose administration. (2) To determine the anatomical location for maximal absorption of lead from the gut, various intestinal segments (stomach, duodenum, jejunum, ileum, or colon) were isolated from groups of 8 animals.The duodenum was isolated after the bile duct was interrupted in an additional group of 8 rats. Test doses of 203Pb containing 1 ug lead chloride were injected into each intestinal loop. Four hours later, the percentage of test dose in the carcass was measured after excision of isolated intestinal segments.(3) The effect of anesthesia on absorption of lead was measured in groups of rats (8 per group) receiving either oral doses of radiolead or injection of radiolead into isolated duodenal loops. Half of the animals in each group were anesthetized with ether and half with sodium pentobarbital.(4) The rate of absorption was tested in 40 rats by injection of test doses of radiolead and 1 ug lead chloride into isolated duodenal loops. Groups of 8 rats were sacrificed at intervals from 30 minutes to four hours after dosing and percentage of test dose measured after excision of the duodenal segment.(5) The effect of age and weight on absorption in isolated duodenal loops was examined in 30 rats of varying ages (79 to 660 g) and weights (recently weaned to more than one year old).(6) To determine whether the total body burden of lead affected the absorption of lead, animals were intraperitoneally injected with either 1 mg of lead chloride or saline (10 rats per group) weekly for six weeks. One week after the last injections, lead absorption studies were performed in isolated duodenal loops.(7) The effects of starvation and dietary protein on lead absorption were studied. Three groups of 8 rats were fasted for variable intervals and lead absorption measured. Subsequently, three groups of 10 rats were placed on diets of similar caloric content but different protein concentrations (0, 5, or 26%) for three weeks and lead absorption was measured.(8) Three groups of 10 rats were fed a diet supplemented with vitamins for three weeks. In two groups, the diet was supplemented with ferrous sulfate (1 g iron per kg) and the remaining group was fed an iron-deficient diet. The rats in one of the iron supplemented groups were iron loaded by intramuscular injection of dextran iron at the beginning of the experiment. After three weeks, rats were fasted overnight and lead absorption studies were performed in isolated duodenal loops.(9) Various dietary constituents (e.g., amino acids, sugars, vitamins, and essential elements) were tested for their effects on lead absorption by adding millimolar concentrations of these constituents to lead in solution so they could complex with lead prior to injection into isolated duodenal segments. (10) Excretion of lead was examined in six rats fasted overnight and given 2 uCi 210Pb in saline by injection into the dorsal vein of the penis. Whole body counting ws performed immediately after injection and at daily intervals for 14 days and at weekly intervals for 10 weeks. Radioactivity in feces and urine was also measured. A similar experiment was performed in three groups of 8 rats in which one group drank distilled water, one consumed water containing 10 ug lead chloride per ml, and the third group consumed water with 100ug/mL lead for one week before receiving an intravenous injection of radioactive lead.(11) Organ localization of lead was examined in 36 fasted rats injected intravenously with 2 uCi 210Pb in 0.5 ml saline. Whole body counting as well as radioactive measurements in blood and individual organs were examined at various intervals after, up to 14 days.(12) Red blood cell incorporation and plasma clearance of lead was examined in 8 rats receiving 2 uCi 210Pb intravenously. Whole blood specimens were collected 5, 15, 30, 60, and 120 minutes after injection and radioactivity was quantified. These studies were repeated using donor rat plasma incubated with 203Pb for 30 minutes to permit binding to plasma proteins before injection.(13) Lead deposition in intestinal segments was examined in 12 fasted rats that underwent laparotomy. In half of the animals, the bile duct was ligated. Intestinal segments were isolated, the abdominal cavity closed, and each rat received an intravenous injection of 2 uCi of 210 Pb in 0.5 ml saline. Four hours later the intestinal segments were removed unopened and prepared for radiolead detection.(14) To examine the effect of lead loading on excretion, three groups of 20 rats were used. One group received 1 mg lead chloride intraperitoneally two weeks before testing, the second group was given the same dose one day before the intravenous injection of 2 uCi 210Pb, and the third group served as a control and did not receive a lead chloride dose prior to testing. Blood and various organs were removed at intervals of 1 hour, 8 hours, and 1, 5, and 14 days after dosing for measurement of radiolead.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Lead acetate

EC Number:

239-379-4

EC Name:

Lead acetate

Cas Number:

15347-57-6

IUPAC Name:

lead(4+) tetraacetate

Constituent 2

Reference substance name:

lead nitrate

IUPAC Name:

lead nitrate

Details on test material:

Radioisotopes of lead were obtained from New England Nuclear (Boston, Massachusetts, United States) as either 203Pb acetate (specific activity 10 to 50 uCi per mg lead) or 210Pb nitrate (specific activity 10 uCi per mg lead).

Radiolabelling:

yes

Remarks:

[203Pb] acetate and [210Pb] nitrate

Test animals

Species:

rat

Strain:

Wistar

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS- Weight at study initiation: 200 to 250 g.- Housing: Animals were housed in galvanized cages or plastic metabolic cages. For experiments in which excreta were collected, animals were housed in individual metabolic cages (Econo Metabolism Unit, Maryland Plastics, Federalsburg, Maryland, United States).- Diet: Commercial rat diet containing 25% protein (Wayne Lab-Blox, Allied Mills, Inc., Chicago, Illinois, United States) unless otherwise stated. Components for special diets were obtained from Nutritional Biochemicals Division of ICN Life Sciences Group (Cleveland, Ohio, United States). Vitamins added to special diets were ICN vitamin diet fortification mixture (3% by weight). In iron deficiency experiments, these vitamins were added to whole powdered milk with or without iron. In protein depletion diets, Jones and Foster salt mixture was also added to the various dietary constituents (4% by weight).- Water: Deionized water, ad libitum.

Administration / exposure

Route of administration:

other: Oral (gavage); injection into isolated intestinal segment; injection into dorsal vein of penis

Vehicle:

other: Water for oral experiments; 0.9% saline for injection experiments

Details on exposure:

Lead absorption experiments were performed in rats fasted overnight. Oral test doses were administered through polyethylene catheter into the stomach. In later experiments, a laparotomy was performed and the duodenum isolated with umbilical tape. In most experiments, the bile duct was isolated, ligated, and cut. One milliliter of a solution containing 1 uCi 203Pb and 1 ug lead chloride (pH 3) was injected into the isolated intestinal segment with a hypodermic needle. The abdomen was closed with sutures and surgical clips and whole body radioactivity was measured. Four hours after administration, animals were sacrificed, intestinal segments were excised, and whole body radioactivity was measured again. In some cases, retained radioactivity was also measured in the isolated intestinal segments.Lead excretion studies were performed in rats fasted overnight and anesthetized immediately before the experiment. Each animal was given 2 uCi of 210Pb in 0.5 ml of 0.9% sterile saline by injection into the dorsal vein of the penis. Whole body radioactivity was measured immediately after dosing and at intervals thereafter. Radioactivity was also measured in urine and feces from each animal. In experiments in which organ retention of readiolead was measured at intervals after the test dose, whole body carcass activity was measured before dissection. Organs were then excised and radioactivity measured.Radioactivity was also measured in blood and in histological sections of opened intestine.

Control animals:

other: Negative controls for certain experiments

Statistics:

Statistical comparisons were made using Student's t-test for the unpaired data. Results were expressed as the mean and standard error of the mean. Half-time disappearance of radioisotopes from various organs was calculated by the best fit slope using mean square analysis on semilogarithmic plot.

Results and discussion

Preliminary studies:

(1) The percentage of the dose absorbed into the carcass was similar in groups of animals receiving 1 ng to 10 ug of the lead chloride carrier, but less radioactivity was observed in animals receiving the larger doses of 100 ug or 1 mg. The decrement in lead absorption between 10 ug and 1 mg was such that a 100-fold increase in the test dose was accompanied by only a 20-fold increase in the quantity of lead absorbed.(2) Lead was most efficiently absorbed in the duodenum (Table 1) and bile enhances the absorption. Radioautographs of duodenal mucosa of rats given oral doses of 210Pb indicated that radioactivity was concentrated in the mucosal cells of the villi.(3) The percentage of radiolead absorbed was similar when ether or pentobarbital anesthesia was utilized, but the quantity of lead absorbed was almost two-fold higher from isolated duodenal loops than from an oral dose.

Toxicokinetic / pharmacokinetic studies

Details on absorption:

(4) Radioactivity was detected (6.5% of the test dose) in the carcass within 30 minutes after dosing but absorption occurred more slowly thereafter. There was no difference in carcass radioactivity between four and six hours after dosing. There was no difference in the amount of radiolead in intestinal segments at any of the intervals studied, suggesting mucosal uptake occurs primarily during the first 30 minutes after administration and significant additional uptake does not occur until mucosal lead transferred to the rest of the body.(5) Absorption of radiolead decreased as animals aged or gained weight (r = 0.89, P < 0.001).(6) There were no differences in absorption between the lead-loaded and control animals (18.84 vs. 18.20%). The intraperitoneal injection of lead chloride from one hour to 14 days before the measurement of lead absorption from isolated duodenal loops did not affect mucosal uptake or absorption into the carcass.(7) Rats fasted overnight and for three days had similar mucosal uptake of lead (12.9 and 13.4%) and absorption into the carcass (19.7% for both). In contrast, animals fasted for five days had decreased mucosal uptake (8.6%) and absorption of lead into the body (8.17%); P < 0.01). Rats on low protein diets (0 and 5% protein) had diminished lead absorption compared to animals on a diet of 26% protein (P < 0.05).(8) Animals on an iron-deficient diet absorbed more lead from the test dose (21.3%) than did the control rats (11.2%; P < 0.01), whereas the iron-loaded animals absorbed less lead than controls (7.71%; P < 0.05). The quantity of radiolead in the duodenal segments was not different among the three groups.(9) Methionine, cysteine, cystine, ascorbic acid, tyrosine, and arginine increased the absorption of radiolead (P < 0.05). Other compounds such as iron chloride, zinc chloride, and calcium chloride decreased the absorption of test doses of radiolead (P < 0.05).

Details on distribution in tissues:

(11) Radiolead was maximally concentrated in all measured organs except bone within one to two hours after injection. 210Pb rapidly disappeared from plasma and was not detectable after the first day of observation. Radiolead was rapidly incorporated into red blood cells within the first two hours after injection. Subsequently, there was a rapid disappearance of radiolead from the red cell mass, with a t1/2 of approximately 12 hours. Approximately 25% of the parenteral dose of 210Pb was incorporated into kidneys, with a t1/2 of about 30 hours. Incorporation into the liver was 10% of the dose, with a t1/2 of about one day. The disappearance of 210Pb in the small intestine approximated the two-day lifespan of mucosal cells, suggesting their exfoliation is a mechanism for lead excretion. Measurements of 210Pb in other organs, including heart, lung, and spleen, showed less than 0.2% of the parenteral dose with a disappearance of radiolead within one to two days after injection. An incorporation of 210Pb was found in bone within one hour after injection and increased during the first day of observations. Subsequently, the amount of 210Pb in bone remained stable over two weeks of observation.(12) Within five minutes after injection of 203Pb, only 11.2% remained in plasma and by two hours only 0.78% of the test dose was in the circulating plasma. Red blood cell incorporation was rapid after injection, so that by five minutes, 14.2% of the test dose was found in circulating erythrocytes. This increased to 18.4% by 30 minutes after injection and remained stable over the next 90 minutes of observation. Similar values for plasma clearance and red blood cell incorporation of radiolead were obtained when the study was repeated using donor plasma incubated with 203Pb before injection.(13) Radiolead was measured in the small intestine with smaller quantities in other portions of the gut (Table 2). Although the greatest amount of radiolead was observed in the duodenal segments, this was caused mostly by biliary excretion of the parenteral dose. In animals with ligated bile ducts, there did not seem to be preferential localization of radiolead to the portion of the gut where lead was primarily absorbed (Table 2). This suggests that bile serves as a pathway for excretion of lead from the body.

Details on excretion:

(10) During the first 24 hours after injection of 210Pb, 24.3% of radioactivity was lost in urine and 8.3% was lost in feces. One week after dosing, rats retained 38.1% of the injected dose and had lost 40% in urine and 21% in feces. Subsequently, there was a slower loss of radioactivity from the animals at a rate with a t1/2 of approximately 180 days. Animals receiving lead supplementation in drinking water retained greater amounts of lead within a few days after injection than those that did not.(14) Control animals lost more radiolead from their whole bodies and had higher concentrations in red blood cells and kidneys than lead-laden animals.

Any other information on results incl. tables

Table 1: Absorption of Lead from Isolated Intestinal Segments

Site	% of 203Pb in Carcass
Stomach	0.88
Duodenum (bile duct intact)	9.73
Duodenum (bile duct ligated)	5.96
Jejunum	3.87
Ileum	2.17
Colon	0.14

Table 2: Percentage of Parenteral Dose of 203Pb in Gut Segments

Site	Bile Duct Intact	Bile Duct Ligated
Stomach	1.21	1.0
Duodenum	5.03	2.03
Jejunum	1.39	1.53
Ileum	3.62	3.92
Colon	1.98	2.17

Applicant's summary and conclusion

Conclusions:

The authors concluded that lead absorption occurs primarily in the duodenum where lead enters the epithelial mucosal cells. Excretion occurs in urine and stool, and bile is an important route of excretion in the gut. Although the body seems to possess mechanisms for excreting lead, these systems are limited and once lead is stored in bone, it becomes relatively unavailable for excretion.

Executive summary:

Methods for studying lead absorption and excretion in rats were presented. Lead absorption occurs primarily in the duodenum where lead enters the epithelial mucosal cells. There is a relative mucosal block for lead with increasing intraluminal doses. Certain substances which bind lead and increase its solubility enhance its absorption. Iron, zinc, and calcium decrease the absorption of lead without affecting its solubility, likely by competing for shared absorptive receptors in the intestinal mucosa. The total body burden of lead does not affect lead absorption. Thus, lead does not have a feedback mechanism that limits absorption. Lead absorption is increased during rapid periods of growth in iron-deficient animals. It is diminished with starvation and in iron-overloaded animals. The excretion and kinetics of tracer doses of radiolead were quantified. Red blood cells seem to serve an important role in transport. Excretion occurs in urine and stool, and bile is an important route of excretion in the gut. Although most of a tracer dose is rapidly excreted, the excretory process is limited permitting lead accumulation primarily in bone.