The sources of bpa exposure

Question 1

a. Identify the beginnings of BPA exposure at the population degree.

– BPA is used as a monomer in the industry of polycarbonates and epoxy rosins, as an antioxidant in PVC plastics and as an inhibitor of terminal polymerisation in PVC.

i. Polycarbonate: BPA is used in compact disc industry, nutrient contact container ( e.g. returnable milk and H2O bottles every bit good as babe feeding bootles ) , plastics dinnerware, medical devices, athletics safety equipment and the auto industry.

two. Epoxy rosin: BPA is used in protective coatings in nutrient and drink tins, food-processing application, structural complexs, electrical laminates, electrical application and adhesives. Besides used in some dental complexs and sealers.

– BPA is used as an intermediate in different chemical reaction in the industry.

B. Identify the major and minor paths of exposure for BPA toxicity.

1. Major paths of exposure

– via contaminated nutrient:

  • Feeding bottles
  • Food and drink containers
  • Epoxy rosin nutrient contact.

– Exposure occur when the ester bond in polycarbonate stuffs is hydrolyzed, let go ofing the monomer which can migrate into nutrient and drink merchandises.

– The hydrolysis rate is additions:

  • at high or low pH
  • at high temperature
  • by storage clip ( migrating BPA accumulate in transcribed nutrient during storage )

2. Minor paths of exposure via environment:

  • – Locally contaminated air
  • – Aquatic environment
  • – Dirt

Question 2

a. Children are identified as the highest exposure group.

b. because kids still in a developmental procedure. So they are most susceptible to BPA.

Question 3

a ) Identify the physiochemical belongingss that may heighten BPA possible to do toxicity

1 ) White solid at room temperature. Depending on the fabrication procedure:

a ) Powder

B ) Snowflakes

2 ) Vaporizes at 25C – due to moo vapour force per unit area

3 ) Mild phenolic smell

4 ) Slightly H2O soluble

5 ) Solubility: 300mg/L

6 ) N-octanol – H2O divider coefficient ( log Kow ) is 3.32-3.64 – Not considered as bioaccumulation potency, since chemicals with a value between 4 and 7 bio accumulate to the greatest grade ( BAIRD,2001 )

7 ) Flash point varies – but is set to be circa 207C

8 ) Not explosive – But there ‘s a hazard for dust detonation

Question 3 ( B )

B ) Since the feature of BPA is somewhat H2O soluble, it can be said that half portion of the compound is more to lipid soluble. Therefore, it can easy traverse the lipid bilayer even though it has a low bioaccumulation potency.

Question 4

a. The systemic handiness of parent compound of BPA or of its metabolite is lower following unwritten exposure is predictable because BPA shows extensive first base on balls metamorphosis in the liver.

B. Observation in inquiry 4 ( a ) may decrease the toxicity of BPA because following unwritten exposure, the systemic handiness is lower and hence increase mutual opposition of BPA. Increase in mutual opposition will increase its H2O solubility and hence increase secernment. Higher secernment will decrease its toxicity consequence and kept the possible toxicity to a minimal degree.

c. BPA metamorphosis is improbable to give a batch of intermediates because metamorphosis is catalyzed by enzymes and ever found in the liver. The metamorphosis occurs quickly as most foreign compound enter the organic structure via the GI piece of land and the portal blood supply goes straight to the liver. Besides, the enzymes are non specific for foreign compound and may hold a major function in normal endogeneous metamorphosis.

d. Metabolite of BPA following metamorphosis:

a. BPA – sulfate

B. 5 – hydroxyl – BPA

e. The toxic authority of BPA metabolites compared to rear compounds is higher because it is all depends on mutual opposition, H2O solubility that lead to rate of elimination of the metabolite. In this instance, the toxic authority is higher because after metamorphosis, the mutual opposition is diminishing and decreases its H2O solubility. Low H2O solubility of metabolites will do it hard to egest and stay in the organic structure and increase its toxic authority.

Question 5

a. Identify the metabolic reactions, enzyme that involved in BPA biotransformation.

Metamorphosis of BPA occurs at liver cell or besides called hepatocyte. Metabolic reaction is glucuronidation. Enzyme that involved is Uridine 5′-diphospho-glucuronosyltransferase UDP-glucuronosyltransferase, UGT or glucuronyltransferase.

The glucuronidation of BPA, via the UDP-glucuronosyl transferases ( GT ) , has been shown to be the major in vivo metabolic tract for BPA in the rat, nonhuman Primatess, and human. This path of metamorphosis consequences in the production of BPA-monoglucuronide, a metabolite that has been shown to be devoid of estrogenic activity.

B. Predict if BPA is likely to undergo Phase 1 or Phase 2? Explain.

BPA is likely undergo Phase 2 reaction. Phase I reactions wholly difference compared to phase 2 reaction. Phase 1 besides termed nonsynthetic reactions may happen by oxidization, decrease, hydrolysis, cyclization, and decyclization reactions. Major enzyme involved in this stage is Cytochrome P450 monooxygenase system.

Phase 2 reactions normally known as junction reactions. For illustration if it is used with glucuronic acid, sulfonates. It is normally detoxication in nature, and involved the interactions of the polar functional groups. Enzyme that involved in this stage 2 reactions is transferees, for illustration UDP-glucuronosyltransferases.

The glucuronidation reaction consists of the transportation of the glucuronosyl group from uridine 5′-diphospho-glucuronic acid ( UDPGA ) to substrate molecules that contain O, N, S or carboxyl functional groups.

Glucuronosyl Structure

BPA Structure

The hydroxyl medieties present on BPA provide functional group for glucuronidation. The ensuing glucuronide is more polar ( H2O soluble ) and more easy excreted than the BPA, upon micturition.

c. How does gender and age modulate BPA toxicity

BPA is age dependent. BPA-glucuronide and BPA concentrations in the plasma were greater in newborns than in grownups proposing an immatureness in the development of hepatic excretory map in neonatal rats. However, the half-lives for the elim $ ination of BPA-glucuronide in plasma were more rapid in neonatal animate beings than in grownups. It is likely due to cut down microflora ?-glucuronidase activity and an absence of enterohepatic recirculation.

For gender, BPA can traverse the placenta and nowadayss in chest milk. So, it can impact the foetus and baby. Bisphenol A ( BPA ) , an hormone disruptor, is employed in the industry of a broad scope of consumer merchandises. The suggestion that BPA, at sums to which we are exposed, alters the generative variety meats of developing gnawers has caused concern. BPA blood concentrations were higher in male than in female foetuss. Here we demonstrate parent BPA in pregnant adult females and their foetuss. Exposure degrees of parent BPA were found within a range typical of those used in recent carnal surveies and were shown to be toxic to generative variety meats of male and female progeny. The scope of BPA concentration measured related to sex differences in metabolization of parent BPA.

d. What are the likely paths for BPA riddance from the organic structure?

The likely path for BPA riddance are via fecal matters, piss and chest milk

e. Why would you anticipate BPA to be eliminated chiefly via fecal remains in rats but non in worlds?

Because BPA shows extensive first base on balls metamorphosis ( chiefly by glucoronide junction ) . Enterohepatic circulation ccurs in rats, it is something that non seen in worlds.

f. Why would you anticipate BPA to perforate maternal placental barrier?

There is a determination by Osamu Takahashi and Shinshi Oishi of the Tokyo Metropolitan Research Laboratory of Public Health, The findings show that the placenta fails to move as a barrier to a potentially toxic compound, 2,2-bis ( 4-hydroxyphenyl ) propane, besides known as bisphenol A or BPA. They discovered that BPA is absorbed and distributed in maternal internal variety meats and foetuss highly rapidly.Chemicals with a lower log Pow ( octanol/water divider coefficient ) , such as diethylstilboestrol and salicylic acid, are more hydrophilic and they more easy traverse the placenta. The log Pow of BPA is 3.3, therefore it crosses the placenta so quickly.

Question 6

a ) Examine the LD 50 values of BPA from experimental informations, how would you sort the acute toxicity potency of the chemical?


B ) State the ague and chronic effects of BPA.

Acute effects includes skin annoyance normally from an industrial beginnings, oculus and rhinal annoyance reported by anecdotal company, every bit good as respiratory piece of land annoyance from employee study performed at Shell Oil Company.

There are no informations available on surveies in homo for perennial exposure, mutagenecity, carcinogenicity or generative effects.

degree Celsiuss ) How did research workers infer that BPA is a generative poison?

The critical consequence of BPA exposure is in the EU hazard appraisal identified as the effects on development of generative variety meats which delayed vaginal patency in female and preputial separation in males after chronic disposal.

vitamin D ) Identify the cardinal mark variety meats for BPA toxicity.

After a long term exposure to BPA, the liver is identified as the mark organ in mice, ensuing in debut of multinucleated elephantine cells. Surveies from one research lab bespeaking that exposure to BPA in the ug scope can do developmental effects on the male mice reproduction system, for illustrations, increased prostate weight and reduced efficiency.

vitamin E ) Identify the bomber organelle aim for BPA toxicity.

Size and karyon of hepatocytes are changed.

Question 7

a. Study Table 1 in the reappraisal provided, female animate beings ( pregnant and non pregnant ) appear to be more susceptible to BPA toxicosis. Explain why, with mentions to the NOAEL and LOAEL values.

Based on Table 1,





NTP ( 1985 )






Nagel et Al. ( 1997 ) and Vom Saal et Al. ( 1998 )



Ashby et. Al ( 1999 )



Cagen et Al. ( 1999 )



Tyl et Al. ( 2002 )




Female animate beings ( pregnant and non pregnant ) appear to be more susceptible to BPA toxicosis where the consequence that can be seen were included arrested development in peripubertal development of the mammary secretory organ, decrease of the weight of the vagina and the absolute volume of lamina propia in womb.

As we can see from the tabular array, for NTP 1985 survey, the NOAEL can non be determined. It ‘s average that we do non cognize the exact highest tested dosage of a substance that has been reported to hold no harmful effects on people or animate beings. It will take to disposal of higher dosage that will do harmful BPA toxicosis.

By utilizing the NOAEL or LOAEL values, when dose response curve is extrapolated, it seems to traverse the X-axis at the beginning instead than at some positive value or dose degree. This means that there is a response at all exposure degrees tested and so within the bounds of analytical techniques available, no safe exposure degree can be seen with assurance. Furthermore, for an experimental survey that produced a NOAEL, it will hold stated the inauspicious consequence to be observed before induction. So, it tends to be safer. Because the absent of NOAEL informations in NTP survey, it is the ground why female animate beings appear to be more susceptible to BPA toxicosis.


( NOAEL ) No Observed Adverse Effect Level is the highest tried dosage of a substance that has been reported to hold no harmful ( inauspicious ) wellness effects on people or animate beings.

( LOAEL ) Lowest Observed Adverse Effect Level is the lowest tested dosage of a substance that has been reported to do harmful ( inauspicious ) wellness effects on people or animate beings.

B. Discuss how BPA uncertainness factor was achieved.

Uncertainty factor is a figure ( equal or greater than 1 ) used to split NOAEL or LOAEL values derived from measurings in animate beings or little groups of worlds, in order to gauge a NOAEL or LOAEL value for the whole human population. It is besides called margin-of-safety ( MOS ) .

Uncertainty factors are used to counterbalance for a lack in cognition refering the truth of trial consequences and the trouble in gauging the wellness effects in a different species and/or in different exposure conditions. As such, the value of the uncertainness factor depends on the nature of the toxic consequence, the size and type of population to be protected, and the quality of the toxicological information, and includes scientific judgements.

In this instance, BPA uncertainness factor can be achieved by comparing NOAEL and LOAEL to the estimated exposure degree. The magnitude of MOS is so evaluated based on adept opinion to see if the exposure is of no relevancy to human wellness, taking into history the different uncertainnesss in the implicit in informations. The MOS is estimated for the clinical effects for different subpopulation, such as effects on the liver and birthrate every bit good as developmental consequence.

Depending on the consequence, the decision drawn in the hazard word picture is different harmonizing to the site of exposure. For illustration, by utilizing SCF sentiment, TDI for female carnal = 50/ 1000= 0.05mg/kg/day is compared to the estimated day-to-day consumptions runing from 0.00048mg/kg/day for grownups. It can be noted that TDI is non exceeded.

Another manner to put exposure bound is by utilizing Entire Daily Intake computation. This is the factor used to find the safe consumption for nutrient additives and contaminations such as pesticides and residues of veterinary drugs and to set up the safe degree in nutrient.

Tolerable day-to-day consumption ( TDI )

= No Observed Adverse Effect Level ( NOAEL ) Assessment Factor ( AF )

Question 8

a. Is BPA an hormone disruptor?

Yes. BPA showing the endocrinal disrupt activity on the EU hazard appraisal papers, scope from 3 to 5 orders of magnitude less powerful than estradiol. It besides interferes with thyroid endocrine in vitro.

b. Relate the statement “BPA is an illustration of a non-steroidal xenoestrogen” with the mechanism of BPA action.

Xeno- means foreign or different. BPA is a xenoestrogen, which is nonsteroidal chemical that can come in the organic structure by consumption or surface assimilation and mime the actions of estrogens activity both in vivo and in vitro. However, its construction is different from the endogenous estrogens. As it imitates the estrogens, it can adhere to atomic estrogen receptors and induces transactivation of estrogen-responsive cistrons. It besides has hormone modulating and besides has the ability to interrupt the normal operation of the hormone system ( endocrinal disrupting activity ) . In in vitro systems, BPA competes with estradiol ( E2 ) for adhering with the ( estrogen receptor ? ) ER? and induces look of Lipo-Lutin receptor ( PR ) and proliferation of MCF-7 human chest malignant neoplastic disease cells. Recently, the in vitro surveies besides showed the formation of estrogenically active metabolite of BPA, which is 4-methyl-2,4-bis ( p-hydroxyphenyl ) pent-1-ene ( MBP ) which is 200-fold more powerful than BPA.

c. Why if BPA probably to detain pubescence and retard spermatogenesis in males?

The major concern sing this endocrine-disrupting chemical is with exposure during critical periods in organ development particularly in the embryo, foetus, and newborn. It is because the development of the organ is coordinated by hormonal signals and break of these signals can take to irreversible alterations in organ function.There are surveies bespeaking that exposure to BPA in the mcg-range can do developmental effects on the male mice generative system. The effects may be increased prostatic weight and reduced sperm efficiency. In study by Tyl et Al, ( 2002 ) they proposed that the decrease in organic structure weight addition is the ground to the hold of pubescence ( NOEAL: 50mg/kg bw/day ) .

d. With mention to additivity or hostility, depict the nature of BPA interaction with estrogen.

BPA interaction with estrogen receptor is linear. It inteact by adhering to the receptor and trip the transactivation of estrogen-responsive cistrons. ER? and other members of the steroid receptor household exhibit a common sphere construction with distinguishable parts responsible for ligand binding, dimer formation, DNA binding, and transcriptional activation. Upon adhering estrogen, the ER-estrogen composite is translocated into the karyon, where it binds to estrogen-responsive cistrons. The estrogen-occupied receptor so interacts with extra written text factors and constituents of the written text induction composite to modulate cistron written text.

Question 9

a. Predict the per centum of A- a weak acid poison ( pKa=4 ) that may absorbed across the stomachic mucous membrane membrane ( pH=2 )

pH = pKa + log [ A- ] / [ HA ]

2 = 4 + log [ A- ] / [ HA ]

log [ A- ] / [ HA ] = 2 – 4

log [ A- ] / [ HA ] = -2

[ A- ] / [ HA ] = 0.01

% of A- = 0.01/ ( 1+0.01 ) x 100 %

= 0.99 %

% of HA absorbed = 100 % – 0.99 %

= 99.01 %

B. Predict the per centum of A that may ionise in the plasma ( pH=7 ) .

pH = pKa + log [ A- ] / [ HA ]

7 = 4 + log [ A- ] / [ HA ]

log [ A- ] / [ HA ] = 7 – 4

log [ A- ] / [ HA ] = 3

[ A- ] / [ HA ] = 1000

% of A- = 1000/ ( 1000+1 ) x 100 %

= 99.9 %

Question 10

a ) Discuss the toxicity of C tetrachloride with regard to bioactivation

B ) Your reply should include all relevant chemical tracts and anticipated toxic terminal point.

Carbon tetrachloride is an of import and widely used industrial dissolver. It was once widely used in the family, in fire asphyxiators, shampoo and dry cleansing. Earlier, CCI4 was even used therapeutically against infections by hook worms and in the 19th century dissolver was used as an anaesthetic and analgetic. After the high potency for acute toxicity became apparent, all these applications evidently became disused. Nevertheless, poisoning with CCI4 still occurs, for illustration by inadvertent consumption.

The major mark variety meats of toxicity are the liver and kidney. In the first few hours of consumption, slight to severe neurological upsets are prevalence ( concern, ocular perturbation, CNS depression, coma ) but besides GI annoyances ( purging, diarrhoea and hemorrhage ) . During the undermentioned twenty-four hours ( s ) liver and kidney toxicity develops. In the liver, toxicity is foremost manifested as steatosis ( fatty alteration of the liver parenchyma ) followed by centrilobular mortification.

CCI4 is a little and lipotropic molecule and hence readily distributes in the lipid compartments of the organic structure. It is metabolized in the liver, and the hints to its toxicity lies in the CYP-mediated bioactivation of CCI4 and the initiation of membrane lipid peroxidation.

Mechanisms Of CCI4- Induces Hepatoxicity:

CCI4 undergoes bioreductive metamorphosis catalyzed by CYP2E1 ( a rare reaction for CYPs ) to the trichloromethyl extremist. This CCI group has been implicated in triping the membrane lipid peroxidation concatenation reaction, as it abstracts a H signifier a fatty acyl residue, ensuing in trichloromethane and an alkoxy extremist formation. This is the major tract, particularly under status of low pO2. In contrast, in the nowadays of high O tenseness, the trichloromethyl peroxy group is formed. This is an highly comparative species that reacts and inactivates CYP2E1 itself ( mechanism-based inactivation or suicide inactivation of CYP ) . The effect is that the staying CCI4 can no longer bioactivated because the CYP signifier involved is irreversibly damaged.

CCI4 toxicity is one of those illustrations that attractively illustrate how a elaborate apprehension of the underlying mechanism of toxicity can assist in developing therapeutics schemes in patients. For illustration an acute poisoning with CCI4 can be treated ( within the first 24hours and before necrosis develops ) by exposing the patients to hyperbaric O to forestall farther bioactivation and lipid peroxidation.

Reductive bioactivation of CCI4 leads to a reactive CCI3 group which can respond with fatty acyl residues and originate lipid peroxidation. At high pO2, the CCI3-peroxy group will destruct the bioactivating enzyme, CYP2E1 by suicide inactivation.


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