End of Section 1 www. Section 2 www. Why Ideal Gas in MB? Not Typical MB problem www. Need complete material? Ideal Gas Exercise 1 www. Visit me at www. Ideal Mixture: Partial Pressure www. MB with Ideal Gases Exercise 1 www. Vapor www. Critical Point www. Gas vs. Value of B www. Compressibility Chart www. Law of Corresponding States www. Compressibility Factor Z www. Compressibility Factor Z Low Pressures www. Compressibility Factor Z High Pressures www. Compressibility Factor Z Exercise 1 www. Kay Rule Exercise 1 www. End of Section 2 www. Felder, R; Rousseau, R. In part, the number of stakeholders and issues resulted from our mandate to proceed in a manner that was inclusive, transparent and collaborative.
As discussed in the stakeholder consultation meetings, the core issues in respect of our mandate were, and are, the modernization of the Act ; promptness of payment; and the effectiveness of dispute resolution. Our mandate did not include, for example, opining on procurement issues, which are not a subject encompassed by the Act , and did not extend to proposing the introduction of or major amendments to other provincial legislation.
On this basis, we determined that a small number of issues, such as financial disclosure during the procurement of projects, bidder exclusion provisions, and the potential passage of false claims legislation, were beyond our remit. Having said this, however, the vast majority of the issues identified during the course of the Review to date have been researched and considered and are addressed in the Report that follows.
It is also important to note the breadth of the issues we have considered in respect of the Act. While certain areas were outside of our remit as noted above, everything within the context of the Act was open to consideration. In fact, we considered potential fundamental changes up to and including repealing the Act itself. Accordingly, the recommendations that flow from our report are aimed at allowing the Act to better achieve its policy objectives and at bolstering certain elements of the Act , such as expediting payment and improving the efficiency of dispute resolution, that have not evolved optimally over the years since In addition, we recommend some relatively new concepts which we believe will strengthen the Act while at the same time supporting the intent of the legislation.
A few words regarding the form of the Report. The Information Package, which was broken down into fourteen categories of issues, was intended to provide the background context for the issues that had been identified up to that point in time. Of course, since the issuance of the Information Package we have conducted the stakeholder consultation meetings and the Advisory Group Meetings, and have received multiple written stakeholder submissions all of which have been posted on the Review website , and this process has allowed us to draw a distinction between the core issues, a grouping of substantive issues, and a grouping of technical issues.
Also, some issues that initially appeared to be distinct from one another have, as our research and analysis has developed, proven to be significantly related. As well, we have decided to recommend that no changes be made to the priorities provisions of the Act , and to recommend that alternative dispute resolution remain voluntary and outside the Act , such that our analysis in regards to these issues does not form part of the Report, but will be posted to the Review website as background papers.
Thus, the breakdown of categories contained in the Information Package has changed, and the reader will readily see that the final Report follows its own organizational structure. Above all, we have in our recommendations attempted to achieve an appropriate balance between competing interests and tensions, hence the title of this Report, Striking The Balance.
Among the linked principles we encountered perhaps the most fundamental was that of regulation versus freedom of contract, however the competing values of cash flow versus collateralization also featured prominently, as did efficiency versus thoroughness in regards to dispute resolution. Generally, there was a need to address a complex set of interacting mechanisms in as practical a manner as possible in the circumstances. In each case, we have attempted to develop a recommendation that is practical and efficient. Having said this, it must also be recognized, and the reader will appreciate, that we have reached the fundamental conclusion that promptness of payment, supported by the remarkable efficiency of adjudication, represents a policy objective that justifies the need to strike a balance that allows for blending these recommended features into the legislation.
As part of this introduction we would like to make one fundamental recommendation. That is, given the breadth and scope of the changes we recommend, a new Act will be created, an Act that will encompass rights and remedies that extend considerably beyond construction liens and trusts, and we suggest this new act be named the Construction Act: An Act respecting Security of Payment and Efficient Dispute Resolution in the Construction Industry.
It is our view that such a change correlates with the changes we recommend, the changes in the industry that have taken place since , and the collective desire to move forward with a modernized piece of legislation. In conclusion, we consider ourselves fortunate to have been selected to conduct the Review, and, with the assistance of the persons mentioned above, we have made every effort to fulfill our mandate. The appointment was announced to the public by the Ministry of the Attorney General. The original deadline was ultimately extended to April 30, Following the Announcement, we set out to design a process that would not only fit the needs of the industry but also would be flexible enough to ensure that the consultation would produce valuable submissions and meaningful dialogue.
The goal was to create an open and transparent process. Ultimately, the process was organized in three distinct phases, as follows:. Phase 1 commenced shortly after the Announcement, in February of Initially, MAG provided a list containing the contact information of various stakeholders that had been involved in the process surrounding Bill We heard from many stakeholders in short order after the Announcement. Ultimately hundreds of people were heard from, representing over 60 stakeholders.
Following the stakeholder identification process, the process of issue identification began. There were more issues than originally anticipated. The Information Package, when issued, contained over 60 issues and sub-issues to be considered by the stakeholder community. Its distribution marked the commencement of Phase 2 of the Review process. At this time, the process of preparing a survey which was to be administered by a third party consultant also began. The results of this survey were used to confirm general submissions made by stakeholders and to analyze the views of the industry generally.
Concurrently with the EKOS process, we began the task of coordinating what would become approximately 30 stakeholder meetings that took place between September and December of The initial timeframes for the performance of these consultation meetings required significant adjustment as the Review did not have the power of subpoena and was required to accommodate the busy schedules of industry representatives in order to complete as many meetings as possible. As a result of the extended timeframe, a request was made to the Ministries to extend the deadline for the report which request was subsequently granted such that an initial extension was given to March 31, , followed by a further extension to April 30, as described below.
The stakeholders were grouped, where appropriate, in order to achieve a more efficient process. These meetings were held at our offices in order to present an accommodating neutral environment for stakeholders to share their views and discuss potential opportunities for modernizing the Act. A representative of MAG attended each of the meetings in order to prepare summaries of the discussion.
Copies of the summaries of the Consultation Process are provided on the Review website. Nearly every consultation meeting generated a new idea or new issue for the Review. As part of the Consultation Process, we invited each of the stakeholders as well as members of the industry generally to provide written submissions in relation to the issues identified in the Information Package. These submissions were extremely helpful and were reviewed as part of the ongoing process leading up to Phase 3. In January , we posted the written submissions on the Review website.
Following the receipt of the written submissions and the conclusion of the Consultation Process, a supplemental issues list containing 27 new or modified issues was prepared. Shortly after, we wrote to stakeholders informing them that the new issues list was available and inviting stakeholders to provide discrete supplementary submissions on these issues. A further tranche of written submissions was then received in relation to these new issues that were also considered in the writing of this Report. All submissions are on the Review website.
The final step of Phase 2 was the formation of the Advisory Group. We invited a group of eminently qualified subject matter experts to participate in 3 meetings to be held between January and March of The Advisory Group was comprised of the following individuals:. Importantly, while we selected the members of the Advisory Group in part due to their alignment with key stakeholder groups, the members of the Advisory Group were not representatives of their aligned interests and were not in a position to make binding commitments.
Rather, they brought to the table an ability to provide the context of multiple stakeholder perspectives. In Phase 3, the Advisory Group meetings were held for the purpose of obtaining input in respect of the issues, and determining whether it was possible to achieve consensus on certain issues, as well as to refine recommendations that were being developed following the Consultation Process.
In order to promote discussion, the Advisory Group meetings were conducted on a confidential basis. In March of , certain members of the Advisory Group asked if it would be possible to add further Advisory Group meetings in order to continue the progress that had been made at the previous three meetings. In view of the potential opportunity to achieve further consensus, we gave careful consideration to the possibility of further meetings and ultimately requested a further extension from the Ministry to provide our Report. Shortly after, the Ministries granted the request for an extension so that this Report could be submitted by April 30, During the entirety of Phase 3, our team has been was extensively engaged in researching certain of the issues under consideration in numerous jurisdictions in addition to our own.
That said we could not have produced this Report without the important and significant contributions of the stakeholder community and the Advisory Group. We extend our thanks to each and every contributor for their hard work and collaborative spirit. The definition immediately prior to the amendment read:. The definition now reads:. This amendment primarily affected electrical and mechanical contractors and suppliers of machinery in manufacturing facilities.
The Court of Appeal also dismissed the appeals, holding that each case would be decided on its facts, noting as follows:. In most cases, the installation or repair of machinery used in a business operated in a building, particularly where the machinery is portable , will not give rise to lien rights under the CLA.
On the other hand, where machinery is installed in a building for the use of a business and is completely and permanently integrated into the building, a lien claim will arise. The issue of portability is now said to be largely irrelevant, at least by some commentators. The broad Ontario wording is atypical in Canada. A third definitional approach involves the use of non-exhaustive lists and exclusions to clear up ambiguities.
Some stakeholders advocated for such lists to be incorporated into the Act ; however, Ruth Sullivan, in her text on statutory interpretation and legislative drafting, cautions that non-exhaustive lists can lead to confusion, and should be used to deal with borderline applications of general terms to illustrate the range of application through the use of examples, to prevent the reading-down of legislation to exclude something that is meant to be included.
In Waste Ltd. The test employed by the courts to delineate between repair and maintenance examines whether or not the work improved the value of the land or constitutes part of a construction project for example, snow removal that is part of regular maintenance would not give rise to lien rights, but snow removal directed by a contractor to clear the way for construction of an improvement to continue would as opposed to typical periodic maintenance.
There is also commentary to suggest that some degree of permanence may be required;  a repair of some permanence could result in an increase in the value of the land, while work such as snow removal that is part of regular maintenance does not increase the value of the land, and should thus be excluded. Again, the element of permanence is important in this distinction. The following chart outlines some of the considerations in relation to the work, but the applicability and weight of each will depend on the circumstances:.
In distinguishing between lienable repairs and non-lienable maintenance, the principal considerations therefore are the permanence of the work, the effect the supply has on the land, building, structure or works, and whether or not it is part of an improvement. For some of these contracts, the physical installation of industrial, mechanical, or electrical equipment may be a relatively small element of the work to be performed under a contract, but the project generally may fall within the definition of improvement because of this work.
At section 6 1 c and d of the New Zealand Construction Contracts Act , the installation and maintenance of communications systems is included. In the other jurisdictions reviewed, the inclusion or exclusion or IT projects is not clear. The treatment of IT projects under the Act was also commented on generally by municipal stakeholders during the stakeholder consultation meetings. In several U. Importantly, though, such lists can create confusion as they generally cannot address every area of ambiguity, and should only be used where there is not a more practical alternative.
An alternative is to utilize the approach of the Income Tax Act. With respect to IT projects, few stakeholders offered submissions. While a specific definition could be included in the Act , as is the case in New Zealand, this would move away from the broad scope of the provision unless incorporated as part of a non-exhaustive list. Those IT projects that are essential to the intended use of the building, structure or works would thus fall within the existing definition.
That said, it would not be advisable to expand the application of the Act to include software solution contracts that are not part of a construction project. Accordingly, the definition should not be revised to include such contracts and the dividing line between what is and is not lienable should be left to the courts.
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AFP projects in Canada trace back to the mids,  after the Act came into force. The owner s will vary depending on the project. For example, in the case of a highway, the owner may be the Crown under the jurisdiction and control of the Ministry of Transportation ,  along with any municipalities that the highway runs through.
Or, in the case of a hospital, the Crown will only be involved to fund the project. According to some stakeholders, the resulting confusion has led to increased costs as a result of liens being improperly registered. Significantly, Infrastructure Ontario has suggested that there be only one owner with respect to an improvement, and that the owner should be the entity that requests the improvement from the contractor.
Other stakeholders have suggested the exclusion of AFP projects from the lien regime of the Act , with mandatory surety bonding of AFP projects. Generally, it was agreed that the current definition does not suit the AFP model. As AFP projects have developed, gaining significant prominence in size and scope, problems have been encountered with applying the provisions of the Act.
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Generally speaking, time is money, and delayed projects give rise to extra costs for all parties. The parties typically look to their respective contractual rights for relief. Some commentators question whether or not there should be lien rights in relation to costs or damages arising from delays. Case law in Ontario is divided as to whether additional costs or damages incurred as a result of delay are lienable.
Recent cases have suggested that additional costs incurred because a project takes longer than anticipated such as labour costs, equipment rental and similar costs of remaining on the job can be found to be the basis for a valid lien. As well, some Ontario courts have found that damages at large, such as lost opportunity costs, loss of profits, or aggravated damages are not lienable. Additional costs incurred offsite such as administrative overhead or lost profit, and even onsite office overhead costs, have also been found not to be lienable on this basis.
Some stakeholders have suggested that it would be useful to clarify what can be properly included within a lien claim. The current definition reads:. Further, courts have consistently held that consultants are entitled to make lien claims where the value of the land is enhanced as a result of their services. Stakeholders identified difficulties in registering liens in certain circumstances, including, inter alia, the following:.
The difficulties associated with certain of these types of projects tend to derive from the nature of the projects themselves. For many of these types of projects, liens do not attach to the premises in any event, as they fall into one of the categories listed in section 16 of the Act as follows:. As well, liens cannot attach to federal Crown lands due to the doctrine of interjurisdictional immunity; the Act , being provincial legislation, cannot intrude on a federal undertaking. In applying section 16 of the Act , difficulties can arise for subcontractors liening facilities in terms of ascertaining the ownership and nature of the property in order to properly make a claim for lien.
In addition, some types of projects involve interaction with different pieces of legislation specific to the project type. As well, projects may involve the construction of multiple structures on a single property or more than one property. If an office has not been prescribed, the lien is given to the ministry or Crown agency for whom the improvement is made. The lien is not registered, but constitutes a charge against the holdback. In addition, liens also do not attach to public streets or highways owned by a municipality or a railway right-of-way pursuant to section 16 3 set out above.
Conversely, municipal lands outside of those prescribed under section 16 3 of the Act can be subjected to a claim for lien by registration against title. Some provinces treat municipal lands similar to Crown lands. For example, in British Columbia, although liens can be registered against municipal lands, lien claimants are prevented by the legislation from forcing a sale of the municipal property that is subject to the lien; instead, the court may give judgment for an amount equal to the maximum liability under the legislation.
Several stakeholders have commented that it is unnecessary to register liens against municipal lands. In this regard, municipalities are not authorized to become bankrupt under the Bankruptcy and Insolvency Act ,  although they can and do take on debt. Under section 17 of the Municipal Act , municipalities are not authorized to incur debt unless it is for the purpose of long-term financing or capital projects.
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Colleges that are enumerated under the Colleges of Applied Arts and Technology Act, are agents of the Crown, thus liens do not attach to their lands under the current legislation. In order to have the ability to grant degrees, an institution must either be authorized to do so under the Post-Secondary Education Choice and Excellence Act. With regards to school boards, section Public school boards in Ontario are registered as not-for-profit corporations, and there is no prohibition in the Bankruptcy and Insolvency Act against their becoming bankrupt.
School board trustees are elected during municipal elections under section 58 of the Education Act. Schools are largely publically financed,  and the Education Act prohibits school boards from having in-year deficits without the approval of the Minister of Education and Training and schools must comply with accounting standards set by the legislature. Public hospitals are non-share capital corporations run by their own boards of directors;  hospitals are not agents of the Crown. Despite their legal status, however, public hospitals are almost entirely publically funded, although may raise their own nominal funds through fundraising initiatives, food sales, and parking income.
In Westeel-Rosco Ltd. The Broader Public Sector Executive Compensation Act, , for example, applies to hospitals, school boards, colleges, and other broader public sector entities for the purposes of managing executive compensation. Specifically, although subheadings a and b represent institutions that can be easily identified, and which clearly constitute public interest entities, subheadings c through h include entities that are not easily identifiable, some of which are not core public interest entities. Generally, the definition raises serious concerns regarding how one would identify such entities with certainty and, in some instances, justify their inclusion within a group of entities the lands of which should not be put at risk of a judicial sale.
Further, identifying which lands are hospital, university, or school board lands can be complex as these institutions typically own multiple buildings for research and services outside of their core mandates. The submissions from the municipal stakeholders were nearly unanimous in supporting not only the continued exemption of transportation and rail projects from the registration of liens, but also in supporting an extension of the exemption to municipal lands generally.
As noted above, most of the responding municipalities, with the exception of the City of Toronto, advocated for municipal lands to be afforded the same treatment as Crown lands in that a lien should not be registerable with respect to municipal lands. Municipalities in Ontario cannot become bankrupt, therefore it is unnecessary to have liens attach to municipal lands, with the ultimate remedy of a court-ordered sale.
The Council of Ontario Construction Associates advocated for changes that closely resemble the regime used in Manitoba and British Columbia. In Manitoba, liens do not attach to the interests of municipalities in municipal lands but constitute a charge against the holdback. Other stakeholders, particularly Prompt Payment Ontario, suggested that this is not a practical issue as Ontario municipalities have not had to sell lands in the past to satisfy lien claims.
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The ability to register lien claims against municipalities benefits the municipalities in that administrative procedures need not be put into place to deal with liens that are given. Given that municipalities cannot become bankrupt, and that a situation where the courts have ordered public lands to be sold to satisfy a lien has not arisen, the additional security provided by registering a lien is unnecessary. Both of these solutions satisfy the concerns raised by stakeholders and maintain the security that the lien provides to claimants. The purpose of the lien is to provide security for those who provide services, materials, or equipment.
For municipal lands, this remedy is unnecessary. In some other jurisdictions, liens either do not attach to municipal lands, or, when they do attach, the land cannot be sold in a judicial sale. Municipal owners cannot become bankrupt under the Bankruptcy and Insolvency Act , and are extremely unlikely to become insolvent, or to be allowed by the province to remain so. As well, the courts are highly unlikely to order the sale of such lands. As a result, the current procedure to register liens on municipal properties is largely unnecessary and unduly burdensome.
The basic principles applicable to preservation, perfection, and expiry are as follows:. The stakeholders raised issues in relation to each of the above principles. As a result, we have considered the following issues:. With certain fairly limited exceptions, lien claimants must strictly comply with the preservation and perfection requirements of the Act.
This is important because it provides public notice to the owner of the improved land or premises, potential purchasers, lenders and any other interested parties that a lien claimant intends to enforce its lien against the premises. As discussed in Chapter 3 - Lienability , subject to the exceptions set out in subsections 34 2 Crown land , 3 public highways and 4 railway right of ways , a lien that attaches to the premises is preserved by registration in the proper land registry office of a claim for lien against the title of the relevant premises.
Under section 31 of the Act contractors have 45 days within which to preserve their liens, counting from the earlier of:. Where there is no certification of substantial performance, or for services or materials supplied after the date of substantial performance, the preservation period for contractors is 45 days from the earlier of:.
Where there is no certification of substantial performance, or for services or materials supplied after the date of substantial performance, the preservation period for subcontractors and suppliers is 45 days from the earlier of:. The mean time for preservation across all states is days. Rhode Island has the longest amount of time at days,  which was increased in from days.
Again, I know I've dealt with clients who - routinely in the building trades, most people are on 30 days' credit, and that seems to be fairly standard these days in many organizations, whether it's the building trades or, in fact, the furnishing of materials for the building trades, people are on 30 days. Well, routinely what would happen is that people would get very close to or slightly over the 45 days before it became obvious that somebody was not going to pay their bill.
By that time, it was too late, because after you're over the 45 days, your ability to file a lien disappears. The result in Nova Scotia was an amendment to 60 days, but there were calls to extend the time period even further. The EKOS survey revealed stakeholder concern about the time period to preserve liens, but the results were mixed. Most of those who expressed concern with the day time period suggested only a slightly longer lien preservation period. There was a clear split between stakeholders in their submissions regarding the question of the adequacy of the day time period to preserve liens.
Those who expressed support for maintaining the status quo include the Canadian Bankers Association,  the City of Toronto,  the Consulting Engineers of Ontario,  Metrolinx,  and the Ontario Society of Professional Engineers. Both expressed the concern that extending the time to preserve would extend the time to receive holdback monies.
Several stakeholders suggested modest increases to the day time period, with most suggesting 60 days to align with modern billing practices:. While the preservation period in Ontario is generally in line with the other Canadian jurisdictions, a number of significant stakeholders recommended an increase to 60 days. We are of the view that 60 days is more consistent with prevailing commercial practice, even if prompt payment provisions are introduced into the Act.
Termination occurs when a party repudiates a contract, either through its internal termination mechanism or due to a repudiatory breach. Currently, only abandonment is listed as is a statutory trigger for the commencement of the lien preservation period under section 31 of the Act : termination is not. In British Columbia, termination is included with completion and abandonment of the head contract as triggers for the commencement of the lien preservation period.
For subcontracts, only completion or abandonment act as triggers. The claimant was thus unable to register its second lien. Termination was specifically addressed by the City of Toronto and Metrolinx. Section 33 of the Act allows the contractor to ask the payment certifier to certify a subcontract as completed. There is a prescribed form for this certificate.
Some stakeholders have proposed that the issuance of the certificate of completion of subcontract be made mandatory, or mandatory at the request of any lien holder, while the majority of stakeholders cited the administrative burden this would cause as a reason to maintain the current regime. The Committee is of the view that the mandatory certification of completed subcontracts would impose an intolerable administrative burden on the industry. In most cases, it is very difficult to determine the date of such completion with accuracy. Furthermore, a mandatory scheme of certification would be an extremely expensive burden for the industry to bear.
To make the system work it would be necessary for the owner or payment certifier to be familiar with the terms of all subcontracts. The provision becomes operative on the request of the lien holder, at which point the payment certifier must determine within 10 days of the request whether the subcontract has been completed.
This British Columbia regime is similar to that suggested by some stakeholders, where the certificate of completion becomes mandatory upon the request of any lien claimant.
Striking the Balance: Expert Review of Ontario's Construction Lien Act
Many stakeholders who responded regarding the issue opposed making the certificate of subcontract completion mandatory. This group included:. All expressed opposition to making the certificate of completion of subcontract mandatory on grounds of unnecessary administrative burden and delay disproportionate to any benefit.
Those stakeholders who recommended making certificates of completion of subcontract mandatory suggested that it become mandatory on request of the contractor or subcontractor. Most stakeholders were of the view that the certificate of completion of subcontract should not be mandatory. While the rationale for making the certificate of completion of subcontract mandatory at the request of any lien claimant is easily understood, the practical feasibility of such a measure, particularly for large projects, is questionable as it would cause owners to incur a not insignificant additional administrative burden.
Furthermore, our recommendations to permit the early release of holdback set out in Chapter 5 — Holdback and Substantial Performance should at least partially relieve the financial burden of the early trades. Overall, we are of the view that the collective recommendations made in this Report provide sufficient benefits to subcontractors such that making a certificate of completion of subcontract mandatory would provide only a limited incremental gain, with considerable negative administrative consequence. As was the case with the lien preservation time period, the perfection time period was thought by some to be relatively short when compared to other North American jurisdictions.
Concerns have been expressed that the limited time available to perfect a lien is a disincentive to early settlement discussions. Conversely, it has been suggested that extension of the time period would only extend the period of uncertainty. The triggering date for perfecting a lien varies by province.
Generally, it runs from either the last day of the preservation period, the date of preservation, or the date of substantial performance, completion, or abandonment of the contract. Most provinces use the date of the registration of the claim for lien as the trigger date, while Ontario is the only province to use the last day of the preservation period. The following chart outlines the perfection periods across Canada, and when those perfection periods are triggered: .
Comparatively, the mean time for perfection in the United States is much higher than in Canada, at days. The maximum time to perfect from the time of completion of a contract varies greatly, from as few as 90 days in Alaska and Tennessee to over six years in Ohio. York Region,  Metrolinx,  Infrastructure Ontario,  and the City of Toronto  suggested keeping the status quo.
However, the majority of responding stakeholders suggested extending the time period for various reasons, including the following:. The effects of marginal or mild zinc deficiency are less clear. A reduced growth rate and impairments of immune defence are so far the only clearly demonstrated signs of mild zinc deficiency in humans. Other effects, such as impaired taste and wound healing, which have been claimed to result from a low zinc intake, are less consistently observed.
Zinc metabolism and homeostasis Zinc absorption is concentration dependent and occurs throughout the small intestine. Under normal physiologic conditions, transport processes of uptake are not saturated. Zinc administered in aqueous solutions to fasting subjects is absorbed efficiently percent , whereas absorption from solid diets is less efficient and varies depending on zinc content and diet composition 3. Zinc is lost from the body through the kidneys, skin, and intestine. Starvation and muscle catabolism increase zinc losses in urine. Strenuous exercise and elevated ambient temperatures could lead to losses by perspiration.
The body has no zinc stores in the conventional sense. In conditions of bone resorption and tissue catabolism, zinc is released and may be re-utilised to some extent. Human experimental studies with low-zinc diets 2. Controlled depletion-repletion studies in humans have shown that changes in the endogenous excretion of zinc through the kidneys, intestine, and skin and changes in absorptive efficiency are how body zinc content is maintained 7 - The underlying mechanisms are poorly understood. Sensitive indexes for assessing zinc status are unknown at present.
Static indexes, such as zinc concentration in plasma, blood cells, and hair, and urinary zinc excretion are decreased in severe zinc deficiency. A number of conditions that are unrelated to zinc status can affect all these indexes, especially zinc plasma levels. Infection, stress situations such as fever, food intake, and pregnancy lower plasma zinc concentrations whereas, for example, long-term fasting increases it However, on a population basis, reduced plasma zinc concentrations seem to be a marker for zinc-responsive growth reductions 12 , Experimental zinc depletion studies suggest that changes in immune response occur before reductions in plasma zinc concentrations are apparent So far, it has not been possible to identify zinc-dependent enzymes which could serve as early markers for zinc status.
A number of functional indexes of zinc status have been suggested, for example, wound healing, taste acuity, and dark adaptation Changes in these functions are, however, not specific to zinc and these indexes have so far not been proven useful for identifying marginal zinc deficiency in humans.
The introduction of stable isotope techniques in zinc research 15 has created possibilities for evaluating the relationship between diet and zinc status and is likely to lead to a better understanding of the mechanisms underlying the homeostatic regulations of zinc. Estimations of turnover rates of administered isotopes in plasma or urine have revealed the existence of a relatively small rapidly exchangeable body pool of zinc of about 1. The size of the pool seems to be correlated to habitual dietary intake and it is reduced in controlled depletion studies The exchangeable zinc pool was also found to be correlated to endogenous faecal excretion of zinc 19 and to total daily absorption of zinc.
These data suggest that the size of the exchangeable pool depends on recently absorbed zinc and that a larger exchangeable pool results in larger endogenous excretion. Changes in endogenous intestinal excretion of zinc seem to be more important than changes in absorptive efficiency for maintenance of zinc homeostasis Separated fats and oils, sugar, and alcohol have a very low zinc content.
The utilisation of zinc depends on the overall composition of the diet. Experimental studies have identified a number of dietary factors as potential promoters or antagonists of zinc absorption Soluble low-molecular-weight organic substances, such as amino and hydroxy acids, facilitate zinc absorption. In contrast, organic compounds forming stable and poorly soluble complexes with zinc can impair absorption.
In addition, competitive interactions between zinc and other ions with similar physicochemical properties can affect the uptake and intestinal absorption of zinc. The risk for competitive interactions seems mainly to be related to high doses in the form of supplements or in aqueous solutions. However, at levels present in food and at realistic fortification levels, zinc absorption appears not to be affected, for example, by iron and copper Isotope studies with human subjects have identified two factors which together with the total zinc content of the diet are major determinants of absorption and utilisation of dietary zinc.
The first is the content of inositol hexaphosphate phytate and the second is the level and source of dietary protein.
Phytates are present in whole-grain cereals and legumes and in smaller amounts in other vegetables. They have a strong potential for binding divalent cations and their depressive effect on zinc absorption has been demonstrated in humans The molar ratio between phytates and zinc in meals or diets is a useful indicator of the effect of phytates in depressing zinc absorption.
At molar ratios above the range of , zinc absorption starts to decline; at ratios above 15 absorption is typically less than 15 percent The effect of phytate is, however, modified by the source and amount of dietary proteins consumed. Animal proteins improve zinc absorption from a phytate-containing diet. Zinc absorption from some legume-based diets is comparable with that from animal-protein-based diets despite a higher phytate content in the former.
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High dietary calcium potentiated the antagonistic effects of phytates on zinc absorption in experimental studies. The results from human studies are less consistent and any effects seem to depend on the source of calcium and the composition of the diet Some examples of recently published absorption studies illustrate the effect of zinc content and diet composition on fractional zinc absorption Table 53 19, Thus, approximately twice as much zinc was absorbed from a non-vegetarian or high-meat diet 24 , 25 than from a diet in rural China based on rice and wheat flour Data are lacking on zinc absorption from typical diets of developing countries, which usually have a high phytate content.
The availability of zinc from the diet can be improved by reductions in the phytate content and inclusion of animal protein sources. Lower extraction rates of cereal grains will result in lower phytate content but at the same time the zinc content is reduced, so that the net effect on zinc supply is limited. The phytate content can be reduced by activating the phytase present in most phytate-containing foods or through the addition of microbial or fungal phytases. Phytases hydrolyse the phytate to lower inositol phosphates, resulting in an improved zinc absorption 26 , The activity of phytases in tropical cereals such as maize and sorghum is lower than that in wheat and rye Germination of cereals and legumes increases phytase activity and addition of some germinated flour to ungerminated maize or sorghum followed by soaking at ambient temperature for hours can reduce the phytate content substantially Additional reduction can be achieved by the fermentation of porridge for weaning foods or doughs for bread making.
Commercially available phytase preparations could also be used but may not be economically accessible in many populations. Populations at risk for zinc deficiency The central role of zinc in cell division, protein synthesis, and growth makes infants, children, adolescents, and pregnant women especially at risk for an inadequate zinc intake.
Zinc-responsive stunting has been identified in several studies 29 , and a more rapid body weight gain in malnourished children supplemented with zinc was reported. Other studies have failed to show a growth-promoting effect of zinc supplementation The initial presence of stunting was significantly associated with an effect of zinc supplementation on height, whereas initial low plasma zinc concentrations were associated with a more pronounced effect on weight gain.
Results from zinc supplementation studies suggest that a low zinc status in children not only affects growth but is also associated with an increased risk of severe infectious diseases Episodes of acute diarrhoea with shorter duration and less severity and reductions in incidence of diarrhoea in zinc-supplemented groups have been reported. Other studies indicate that the incidence of acute lower respiratory tract infections and malaria may also be reduced by zinc supplementation.
Prevention of sub-optimal zinc status and zinc deficiency in children by an increased intake and availability of zinc could consequently have a significant effect on child health in developing countries. The role of maternal zinc status on pregnancy outcome is still unclear. Positive as well as negative associations between plasma zinc concentration and foetal growth or labour and delivery complications have been reported Results of zinc supplementation studies also remain inconclusive Interpretation of plasma zinc concentrations in pregnancy is complicated by the effect of hemodilution, and low plasma zinc levels may reflect other metabolic disturbances Zinc supplementation studies of pregnant women have been performed mainly in relatively well-nourished populations, which may be one of the reasons for the mixed results Table 53 Examples of fractional zinc absorption from total diets measured by isotope techniques Subject characteristics ref.
Experimental zinc repletion studies with low zinc intakes have clearly shown that the body has a pronounced ability to adapt to different levels of zinc intakes by changing the endogenous zinc losses through the kidneys, intestine, and skin , The normative requirement for absorbed zinc was defined as the obligatory loss during the early phase of zinc depletion before adaptive reductions in excretion take place and was set at 1.
To estimate the normative maintenance requirements for other age groups, the respective basal metabolic rates were used for extrapolation. In growing individuals the rate of accretion and zinc content of newly formed tissues were used to obtain the data required for tissue growth. Similarly, the retention of zinc during pregnancy and the zinc concentration in milk at different stages of lactation were used to estimate the physiologic requirements in pregnancy and lactation The translation of these estimates of absorbed zinc to requirements for dietary zinc involves several considerations.
First, the nature of the diet i. Second, the efficiency of absorption of potentially available zinc is inversely related to the content of zinc in the diet. The review of available data from experimental zinc absorption studies of single meals or total diets resulted in a division of diets into three categories - high, moderate, and low zinc bio-availability - as detailed in Table 54 It was then discovered that the relationship between efficiency of absorption and zinc content differed for these diets Algorithms were developed 32 and applied to the estimates of requirements for absorbed zinc to achieve a set of figures for the average individual dietary zinc requirements Table The fractional absorption figures applied for the three diet categories were 50 percent, 30 percent, and 15 percent, respectively.