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Successful spawning is only the beginning, however, the eggs must hatch, and these reared successfully to fry stage. These stages - spawning, hatching, and early rearing are like a steeple chase which the farmer must win.

The race course is well filled with obstacles, for example physico-chemical quality of water such as available dissolved oxygen, feed of the proper nutritive composition and particle size, low resistance to diseases, and so on.

A good appreciation of all these factors is needed for successful production of fish. The ultimate goal of the fish farmer is to produce fish that meet both his needs and the market demand. Through artificial propagation, the farmer can select for desirable characteristics such as fast growth, resistance to disease, etc.

By hybridization and selection, these goals can be achieved if the farmer dedicates enough time and patience. As stated in the introduction, fish farming begins with the stocking of fry, and these can come from the wild or be produced on the farm. Whatever their origin, they are indispensable and the means of obtaining them influences directly farm production. If supplies are erratic, there will be interruptions in other farm activities; if the supplies are regular, farm production may be maximized.

The cost of the fry can vary considerably and may be an important factor in overall production costs. It any event; a good supply of fry is essential for successful fish farming. If one looks at production of eggs, larvae, and fry that is carried out on the farm itself, the major problems are obtaining a sufficient number of eggs, a good hatching rate of these eggs, and good survival and growth of the larvae obtained.

In nature, there is very high mortality at these stages, and a lot of attention and effort is needed to overcome these difficulties. To practice reproduction and fry production, a certain investment in equipment, infrastructure ponds, tanks, water supply , and trained labour is needed. These costs can be considered a part of overall production costs of marketable fish. The proportion of total cost in producing saleable fish that is met by seed production should be kept always in mind, and efforts made to find new methods of seed production that are less expensive, hopefully increasing the profitability of the whole farm.

For certain farmed fish, it is not yet possible to understand and control all the stages of reproduction, and farmers depend on natural supply. In most cases, these fish are brackish water species and their biological cycle includes migrations into a different environment, either moving to the sea, or into fresh water. Thus to simulate the conditions needed for natural reproduction, this would mean a complete change in the environment.

In general, fish can only be reproduced on the farm if conditions that correspond to natural spawning can be closely approximated. The cost of creating a completely marine habitat or freshwater habitat in the midst of a brackishwater situation would in most cases be prohibitive.

Collecting eggs or fry from the wild was the first method used in obtaining stocking material. This is still occuring for species for which the spawning behavior is not controlled or not well understood, or for which the costs of artificial propagation are too high or where fry in large quantities is easily obtainable.

Means of collection differ with species. Three important species of fish will be examined. Throughout West Africa, the catfish Chrysichthys spp is very popular and in Ivory Coast represents an important species in brackishwater lagoon aquaculture.

As it is relatively difficult to reproduce this fish in captivity, eggs are collected from the wild by placing bamboo traps in areas where this fish C. The traps are placed on rocky bottoms, in deep water 4 — 6 m , by fishermen and the catfish spawns inside the bamboo tube. This method allowed the collection of up to , eggs even outside of the peak spawning periods.

The eggs are transported to the hatchery, and placed in artisanal Zoug jars made from empty plastic bottles. Two or three days after hatching, the larvae are transferred into tanks made of plywood and covered with polyester resin measuring 2.

After about 10 days, the yolk sac is resorbed. After two and half months, they reach an average weight of to mg. During this time, they are fed on a mixture of cattle brain and crab eggs, finely ground which forms a colloid suspension in the water easily accessible as food for all fish. The concrete tanks are 3 m in diameter with a central drain. After the 4th month, the fish are fed with a mixture richer in flour: Percentages are in relation to weight of crab.

The fish are then transferred to enclosures when they achieve an average weight of 4. The fry are reared in enclosures until achieving a size of 50 g, which takes a further 6 months.

The obvious cost and time necessary for procurring catfish juveniles through this method is considerable, and further experimental work is necessary Ledoux, ; Bailly, Larger fish are sometimes captured from the wild. In Nigeria, the catfish are captured using hook and line with soap as bait.

The catfish are injured, and care must be taken to avoid mortalities. It is easy to capture large numbers of catfish using traps to collect fish attracted to tilapia cages Campbell, comm. The milkfish Chanos chanos is found in warm waters of the Red Sea, and the Indian and Pacific oceans and is one of the most important brackish water species cultured particularly in S. In Africa, it is only found on the east coast. The fish reproduces once or twice a year in coastal marine waters of 25 m in depth.

Each female spawns 1. Salinity isn't too important 10 to 32 ppt and the fish are captured where phytoplankton is abondant. When the fry have achieved 1. At this life stage, their diet is a mixture of blue-green algaes and the associated organisms bacteria, protozoans.

The diet will change later on. Artificial reproduction has been achieved in the laboratory, but not yet on a large scale, and thus almost all of the milkfish larvae are captured from the wild. For example, in , in Taiwan only, million fry were captured from the wild Huisman, According to the regions, capture techniques and material can differ.

In Java, the best collection zones are on the north side of the island, and the fry are abundant 7 months out of the year. The best time for capture is at the spring tide, and the three days before and following the full moon.

Sandy beaches, a slight slope, and clear, calm water are ideal. The fish are often concentrated in the zone near estuaries where the influence of freshwater is high.

They will often take refuge leeward of sand bars. If no sand bar exists, the fishermen will build a rock wall perpendicular to the beach into the ocean, or build artificial shelters using palm branches.

As the fry are collected, they are transferred into basins or similar containers, and the sea water is immediately diluted with freshwater. This will kill off many of the other organisms inadvertantly collected, and also acclimate the fry to brackishwater. Other species of fish are also captured, and these must be sorted out. This needs a certain level of expertise and experience on the part of the fisherman. In the Philippines, the fry are captured by using seine nets or traps.

In Mauritius, the fry are captured usually in July using a fine mesh seine net, and are transferred into acclimatization tanks. The mortality is usually high in the tanks Bardach et al , ; Iversen, Mullet species are cultivated around the world, and have a large distribution. Mullets belong to the genera of Mugil or Liza , many species are known. The artificial reproduction is possible, however there are still many instances where fry available in important quantities is collected from the wild.

The mullets reproduce in the sea, and will thrive well in the sea, in estuaries, in brackishwater, and sometimes migrate to freshwater. When they are sexually mature, they form schools, and the reproductive products are released into the sea where the fertilization occurs.

The eggs are pelagic, and hatch in the following two days. After hatching, the larvae begin to swim near the coast where they usually arrive in mass after 2 months. At this point, they have reached a size of 25 mm. On the coast, they form small schools and begin to move towards the estuaries. The capture is usually done as they enter the estuary, at low or rising tide, using seine nets, deep nets, etc.

The fish are euryhaline and have a good resistance to abrupt changes in salinity Bardach et al , ; Iversen, Among the shrimps used in aquaculture, there are two main groups, the Penaeidae and the Caridea. Their biology and life cycles are different. For an example of the Penaidae, Penaeus notialis is widespread and often farmed. Spawning is carried out in the sea and the female is recognized by well developed ovaries and coloration.

She molts shortly before spawning. The male places a spermatophore on the female theca which is kept until egg deposition. The various stages of post egg development occur in the sea. After roughly 3 weeks, the young, termed post-larvae, begin to migrate to estuaries. The larvae are attracted by light, and are often collected by seine nets and deep nets at night.

In other instances, the farm is filled with water known to contain large numbers of postlarvae. Larvae can also be collected by using bunches of palm or coconut branches lashed together and placed on the bottom of the lagoon. After a few days, the traps are surrounded by a fine mesh net and the branches removed. For the group of Caridea, the principal species raised is Macrobrachium rosenbergii.

This species spends its life in brackish-water or freshwater, and migrates to the estuaries or lagoons for spawning. Either gravid females or post-larvae are captured. Again traps, deep nets, etc. In certain cases, it is not possible to reproduce fish species in captivity however; but the capture of fry from the wild presents some problems.

Sometimes the sorting out of species at the fry or fingerling stage is difficult, which will result in a mixed stocking population of different species - some fast growing, some slow growing, some predators and some competitors also - into the pond. Identification keys for fry and fingerlings are not often available. Diseases and parasites affecting wild fish can be introduced into the pond. On the other hand, fry collected in nature have usually already passed the most critical stages of their life cycle where the mortality is highest, and have good survival rates when stocked.

If reproduction and larval rearing is carried out on the farm, each problem at each step of the whole process must be solved.

This may be expensive if infrastructure, equipment and skill is needed. For some species, as tilapia, however, not much is needed. However, if using natural stocks, their abundance and demand will vary the price, and some years, the fry availability may be very low.

Optimum collection periods will vary from year to year, and the ponds may not be properly prepared when the fry becomes available.

In the two cases, it is important to have a sound understanding of the biology of the fish species either to duplicate reproductive conditions on the farm, or to know when and where to collect the fish. The necessary time spent in studying the fish, in collecting the necessary data on reproduction, etc, and then procuring the necessary equipment for capture may in the end be as expensive as artificial reproduction.

There are many different forms of controlled reproduction, but all achieve the result of fertilized eggs. In some cases, the adult fish are captured from the wild, in other cases, the fish come from the farm itself. Perhaps the most important fish where the mature broodstock are captured from the wild are the atlantic or pacific salmons, where the gravid females and ripe males are captured on their spawning migration into freshwater rivers.

These fish will die after a single spawning. The females are captured, either the eggs are stripped, or in some cases the ovaries removed and the eggs obtained through killing the fish, and the eggs are fertilized with milt of males captured at the same time.

In Europe, gravid pikes Esox lucius and catfish Siluris glanis are captured in their natural spawning habitats. Gravid sturgeon females are collected for preparation of caviar. If broodstock is not to be sacrificed, care must be taken not to injure the usually large fish. Actually the only fish species with potential future for aquaculture in Africa where the broodstock is captured from the wild for breeding in pond is the mullet. Hybridization of mullets different species have been achieved with that technique.

Collection of broodstock or adult fish is always an alternative, if no selected strain is available or if inbreeding is to be avoided. Generally, the broodstock used in artificial reproduction will come from the farm. In this way, the farmer can choose and select his fish in view of genetic improvement. The sexes are usually kept separate, and the broodstock feed with a diet optimum for egg production.

The size and age of this broodstock will of course vary with the species and geographic location, temperature and the management techniques of a particular farm. Broodstock must be prepared for spawning, and this is why they are usually kept in special broodstock ponds.

Sexual maturation is a process, usually directed by external factors temperature, photoperiod, water depth, salinity, pH etc with a corresponding internal change brought about by hormonal activity. Proper health of the fish can be assured by adequate feeding of the broodstock for a sufficient time before spawning occurs. Separation of fish according to their sex for some time prior to spawning is generally beneficial for Clarias spp. Length of photoperiod is also important but not for equatorial species, where the change of length of days according to the solar year is minimal.

Light conditions of the breeding environment play also an important role, some species breed in day light, other in the dark. Catfishes prefer muddy water than brightness.

Water conditions must also be optimal as regards to D. Stocking densities should be low, to assure e some quietness to the fish, avoiding stress and disturbances, that may affect the fish and the maturation of the gonads Woynarovitch et al , Feeding of brood stock is important, although not much information is available on the specific needs for feeding broodstock.

Most of the research has been done on the effects of a lack of particular nutrients in the diet. Carotencides are present in maturing ovaries. They are mobilized from the muscles and transferred and concentrated in the ovaries. Deficiencies of Vitamin A or carotenoides in the female will decrease the chances of survival of the eggs and the larvae Shehadeh, During maturation, there is an accumulation of non saturated fatty acids in the ovaries and increase of level of protein and dry matters.

If sufficient feed is not given to the broodstock, there will be some cellular modifications in the hypohysis and a reduction of secretions in gonadotropins. This shows the need for proper feed during the period prior to the breeding. Some aquaculturists recommend to avoid too fatty diets, as fat accumulates in the tissues and affects the breeding Shehadeh, Feed given to breeders after spawning brings about deposition of fat and protein in the tissues which will be used for subsequent vitellogenesis.

In this context, the function of anabolic estrogens, of prolactine and thyroxine in the process of vitellogenesis is not well understood and would need further studies.

Estrogens present in the feed of females has a negative effect on the development of the ovaries and can cause sterility if the level of estrogens is high enough. There is need to be careful with some of the oilcakes, which contain naturally high levels of estrogens Sundararaj, One should check the levels of natural anabolic estrogenes present in some food stuffs as this may interrupt the spawning process.

In general, the effects of feed on broodstock are little understood, and more work needs to be done in this area. As a general rule, feed should be a composite using as many different ingredients as is feasible to avoid any unknown deficiencies or excess that may be present if fish are fed only one ingredient. Protein, lipids, calcium, phosphate should be high enough to allow for egg yolk production. The reproduction of a species has to assure the survival of the species see Fig.

The development of the oocytes is a long process that occurs over a relatively long period of time, and spawning occurs when the moment is the best for the survival of the fry, abundant food, shelter etc see Fig. Reproduction is controlled by internal factors intrinsic and environmental factors extrinsic. When the fish is about to breed, proper environmental conditions are not enough to get the process of spawning started. There is need for the female to encounter a male in the place suited for laying the eggs.

Often the behaviour of male and female has to be coordinated in such a way that male and female of the same species come close to assure fertilization of eggs by the male's milt. The adjustment of the respective movements to this effect is fixed in the specific pattern of the breeding behaviour. Sometimes this behaviour is quite elaborate, as for tilapias, and is extended beyond the time of laying the eggs to the time the fry is able to sustain on their own and provide to their own needs.

Adaptation for the survival of the species - Reproduction After Woynarovich and Horvath, Hormonal control of reproduction is controlled and relayed by the excretion of successive hormones by various centres of the fish. The environmental stimuli are received by the brain, which transmits to the hypothalamus which transmits to the pituitary, which transmits to the gonads, which produce the sexual hormones see Fig.

Control can be obtained at three levels, the hypothalamic, pituitary, or gonadal level see Fig. The technique used most frequently is the use of pituitary extract hypophysation. The pituitary gland is extracted, and can be conserved in either, alcool, or glycerine. Various techniques have been developed and can be found in the literature, particularly for Indian carp culture see Fig. The whole pituitary gland can be used fresh or dried; it is ground, placed in a suitable solvent, centrifuged, and the supernatant is injected into the female fish and sometimes the male Fig.

Actually, purified gonadotropins from pituitaries are also used and commercialised. Ohter hormones in use are mamalian hormones, which are available in most pharmacies. Human chorionic gonadotropin HCG is most frequently used, although some success has been possible using luteinique hormone LH or FSH, follicule stimulating hormone. The gonadotropins, isolated with varying degrees of purity from fish, are glycoproteins, the composition is similar to mamalian LH.

However, the researchers are not yet in agreement whether there exists only one or two gonadotropins, as is in the case of mamals. Probably there are two; one hormone controlling vitellogenesis, and another for the final maturation and ovulation. Vitellogenesis begins with a mobilization of fats, which are synthesised into glycophosphoproteins in the liver, and are deposited into oocytes.

This action is supported by the sexual hormones produced by the ovary. The gonadotropins act on the follicule tissue of the ovary to produce an ovarian steroid, which in turn stimulates the maturation and ovulation. The estrogenes themselves stimulate the synthesis of vitellogenine, a glycolipophosphoprotein in the liver.

The mechanisms of action and retroaction of hormones guiding reproduction are then very complex, and can vary between species. The most common symptom is pain in the right upper part of the abdomen. Because the pain comes in episodes, it is often referred to as an "attack.

Warning signs of a serious problem are fever, jaundice, and persistent pain. When to Seek Medical Care for Gallstones. If a person has an episode or recurring episodes of abdominal pain 30 minutes to one hour following meals, call a health care practitioner for an appointment.

Go to a hospital emergency department if the person has this abdominal pain with any of the following conditions: Upon hearing the patient's symptoms, the health care practitioner will probably suspect gallstones.

Because the symptoms of gallbladder disease can resemble those of other serious conditions, he or she will ask the patient questions and examine them to try to confirm this diagnosis and rule out other conditions.

Ultrasound is the best test to examine the gallbladder for stones. These tests are the alternatives to ultrasound and OCG. They are better choices if gallstones have left the gallbladder and moved into the ducts.

A chest X-ray may be performed to make sure there are no other reasons for the abdominal pain. As most gallstones are asymptomatic, many times gallstones are diagnosed when the patient undergoes a test for another reason. After a diagnosis of gallstones, the patient may choose not to have surgery or may not be able to have surgery right away. There are measures the patient can take to relieve the symptoms to include:.

Call a health care practitioner if symptoms worsen or if new symptoms appear. Abdominal pain with vomiting, fever, or jaundice warrants an immediate visit to a doctor's office or a hospital emergency department.

There is no permanent medical cure for gallstones. Although there are medical measures that can be taken to remove stones or relive symptoms, they are only temporary. If a patient has symptoms from gallstones, surgical removal of the gallbladder is the best treatment. Asymptomatic producing no symptoms gallstones do not require treatment. Extracorporeal shockwave lithotripsy ESWL: A device that generates shock waves is used to break gallstones up into tiny pieces. The results of this study were consistent with other research into the cancer risks associated with TCDD.

A recent scientific review article noted that " a number of large-scale retrospective cohort mortality studies have found significant increases in cancer mortalities all types of cancer combined. These increases were typically found in workers exposed to the highest levels of dioxin [TCDD] and in workers with the longest follow-up periods. In general, the standardized mortality ratios were low less than 1. For illnesses other than cancer, a recent scientific review article indicates that the evidence from human studies has not been strong enough for example, the results are inconsistent or the studies are not designed well enough to estimate specific risks associated with TCDD exposure.

A more detailed discussion can be found in the article, which concludes that " although more than a dozen different adverse effects have been reported in various studies of humans in the past 25 years, the most consistent clinically important adverse effect of human exposure appears to be chloracne " Greene et al.

Chloracne is a skin condition. Typically, this condition is only observed in people when the TCDD level in their blood is several thousand times greater than the levels typically seen in the general population Greene et al.

Veterans involved in herbicide handling and spraying in the Vietnam War were exposed to a number of different herbicide formulations see "What is Agent Orange? Health studies of these veterans therefore look at the potential long-term health effects of herbicide exposures in general.

These exposures were mainly to Agent Orange, but exposure to other herbicide formulations, such as Agent Purple, also occurred. In comparison to heavily exposed industrial workers, Vietnam veterans were generally exposed to lower levels of TCDD.

It is estimated that t he maximum TCDD dose experienced even by the US Air Force personnel directly involved in spraying "Ranch Hand" veterans was about one tenth of the maximum predicted dose of industrial workers Akhtar et al.

The most recent study of death among U. Army veterans in general concluded that death rates due to chronic conditions, such as cancer or heart disease, were no different in veterans who served in Vietnam as compared to non-Vietnam veterans Boehmer, For the vast majority of Vietnam veterans, unless they were directly involved in the handling and spraying of Agent Orange, their exposure to Agent Orange would have been very small Young et al.

The greatest degree of Agent Orange exposure in Vietnam would have occurred among those veterans who directly handled or sprayed Agent Orange: Army Chemical Corps veterans were involved in the storage, preparation, and application of a variety of herbicides in Vietnam.

In a recent study, the death rate among Vietnam Army Chemical Corps veterans was not significantly different than non-Vietnam veterans for all causes, circulatory disease, or cancer. Vietnam veterans in this group had a higher risk of dying due to digestive system diseases, largely cirrhosis of the liver, as compared to non-Vietnam veterans. The authors noted, however, that their study design did not account for lifestyle factors that can also cause cirrhosis of the liver, such as alcohol use: The Vietnam veterans' risk of death from digestive system diseases, including cirrhosis of the liver, was not higher than the risk for the general U.

The aerial spraying of herbicides in Vietnam was conducted under the name "Operation Ranch Hand", from to Air Force veterans who took part in Operation Ranch Hand handled and sprayed herbicides, and they are the Vietnam veterans with the greatest exposure to Agent Orange. These veterans have been studied closely in the Air Force Health Study, the purpose of which was to determine if the health of veterans who handled and sprayed herbicides in Vietnam had been harmed by this exposure.

The Air Force Health Study was launched in and t he most recent and reportedly final report was released in July see http: May to March " to access the full report. The Air Force Health Study examined more than health-related outcomes in these veterans, grouped broadly into 12 areas.

The overall significant findings in each area can be found in the executive summary of the report and are summarized below. Measures of general health were not related to herbicide exposure. The one exception was that body mass index a crude measure of body fat was greater with increasing blood TCDD levels.

Mixed patterns of associations were found, but no consistent or meaningful patterns that would suggest that herbicide exposure caused cancer. The report stated that " these patterns did not suggest an adverse relation between cancer and herbicide exposure". Of the many neurological tests that were performed, only differences in pinprick sensation and reflexes were observed in those with the highest TCDD exposure, providing " some support for a relation between dioxin [TCDD] exposure and peripheral nerve function ".

No measures of psychological health were associated with herbicides or TCDD exposure. Of the many tests performed, there was no association between the gastrointestinal test results and herbicide or TCDD exposure. The only exception was a relation between TCDD and higher levels of triglycerides, a type of blood fat.

Although measurable, this relationship was not considered to be of any health significance. A variety of health outcomes were studied, such as heart attacks, heart disease, vascular disease, strokes, and high blood pressure.

The report concluded that " overall, cardiovascular health did not appear to be adversely associated with herbicide or dioxin [TCDD] exposure ". Several factors were measured in the blood of Ranch Hand veterans. Overall, there was no indication of an " adverse relation between herbicide or dioxin [TCDD] exposure and any haematological [blood disease] diagnosis ".

There was no indication of " adverse relation between renal [kidney] function and herbicide or dioxin [TCDD] exposure ". There was a slightly increased risk of Type 2 adult-onset diabetes among the Ranch Hand veterans with the highest exposure.

There were no consistent findings relevant to health for thyroid or sex hormones. There was no consistent association of health significance between any measure of immune function and herbicide or TCDD exposure.

There was no association between lung health and exposure to herbicides or TCDD. The Air Force Health Study report concluded that overall, only type 2 diabetes was associated with exposure to TCDD among these veterans with the greatest herbicide exposure. The Ranch Hand veterans were not more likely to be diagnosed with Type 2 diabetes than the comparison veterans without significant herbicide expsoure, but their risk of Type 2 diabetes increased with increasing blood TCDD level.

The study confirmed associations between diabetes and other known risk factors: The report noted that " the epidemiologic studies suggest that any increased risk of Type 2 diabetes from herbicide or dioxin [TCDD] exposure is small when compared to the known predictors - family history, obesity, physical inactivity - for diabetes ". The IOM has also found limited or suggestive evidence of a link between adult-onset Type 2 diabetes and herbicides used in Vietnam, including Agent Orange, but concluded that other traditional risk factors for diabetes far outweigh the risks of Agent Orange.

The most recent study of causes of death among Ranch Hand Vietnam veterans was published in May Compared to Vietnam veterans who did not spray herbicides, Ranch Hand veterans did not have a greater risk of death due to cancer. When all Ranch Hand veterans were examined, the risk of death from all causes and from circulatory disease was slightly increased, but this was not statistically significant in other words, chance could not be excluded as the reason for this slight increase. When only enlisted ground crew were examined, they had a slightly greater risk of death due to circulatory diseases than the comparison veterans.

However, when veterans with serum TCDD measurements were examined, the risks of death from all causes, from cancer, or from circulatory disease were not significantly increased. In other words, those with measurable TCDD exposure did not have a greater risk of death from any cause compared to Vietnam veterans without significant herbicide exposure Ketchum et al.

More information is available from the Air Force Health Study website http: As a result of political and policy decisions, the US Veterans Administration automatically presumes that veterans who served in Vietnam were exposed to Agent Orange http: They are also required by law to presume that, if a veteran develops an illness that is among those associated with Agent Orange, the illness is related to military service Section 2, US Agent Orange Act of , Public Law No.

The IOM notes that they have not found that Agent Orange is the cause of any illness, that the associations they found were largely based on studies of heavily-exposed chemical and agricultural workers, and that their conclusions " are not intended to imply or suggest policy decisions ".

Veterans Affairs Canada grants pensions for service-related disabilities, with the pension process designed to give applicants every chance to show how their disability is related to military service. Veterans Affairs Canada requires evidence of exposure and a medical diagnosis of the condition ie. Pension Adjudicators take into account the latest scientific evidence available to establish an association between the condition and exposure to Agent Orange during service.

Pension Adjudicators have flexibility in weighing the evidence presented in individual cases and, in the absence of credible evidence to the contrary, any doubt that arises in weighing evidence regarding a service-related illness associated with exposure is resolved in the applicant's favour. In fact, the Department is obliged, under the Pension Act, to give the "benefit of the doubt" to the Veteran.

The environmental fate of Agent Orange has been described in a recent review article Young et al. For Agent Orange to be as effective a herbicide as possible, the maximum amount of spray had to reach the vegetation as quickly as possible.

To achieve this, aircraft flew very close to the treetops in calm weather conditions to minimize the amount of spray drifting outside of the target area. Rapid settling of the spray droplets was also important. Droplets of this size generally fall rapidly. US studies showed that even the droplets smaller than m m would have hit the vegetation less than 3 minutes after spraying Young et al.

For spray drift beyond the target area to occur, herbicide would have to remain in the air for extended periods of time, where it would be rapidly degraded by sunlight. Aerial photographs of herbicide-sprayed areas in Vietnam show very distinct and sharp lines between treated dead and untreated healthy trees. Had there been significant drift either way from the swath of aerial spraying, traces of damage would have been visible as streaks of discoloured foliage Young et al.

The studies showed that little aerially-sprayed Agent Orange reached the forest floor as liquid droplets. The Agent Orange that lands on plant surfaces is absorbed into the wax layer of the plant cuticle within minutes and cannot be physically dislodged Young et al. Agent Orange left on the plant surface breaks down in sunlight within hours Crosby et al. It is estimated that very little, if any, Agent Orange can be dislodged from the plant surface 24 hours after spraying Young et al.

It is likely that due to the degradation by sunlight of TCDD on leaf surfaces that little material would be left by the time the leaves fall to the ground. TCDD is not very soluble in water and binds tightly to soil particles. Estimates of the half-life of TCDD the amount of time it will take for the concentration of TCDD to be reduced by half on the soil surface range from 9 to 15 years, whereas the half-life in subsurface soil may range from 25 to years ATSDR, However, TCDD may enter surface water secondary to soil erosion and runoff.

Although some of the TCDD that makes its way to surface waters will be broken down by sunlight or evaporate, most will remain strongly attached to small particles of soil or organic matter and eventually settle to the bottom. TCDD attached to this organic matter may enter the aquatic food chain. Small aquatic organisms absorb TCDD that is attached to sediment and organic matter in bodies of water.

Larger fish then consume these smaller organisms and accumulate TCDD in their fatty tissues. Root uptake and translocation to upper plant parts is very minimal. Herbicide testing was conducted at Eglin Air Force Base in Florida from to , when roughly 75 kg of 2,4-D and 76 kg of 2,4,5-T the ingredients of Agent Orange were aerially sprayed on an area of less than 3 square kilometres. It is estimated that 3. Because of the extent of the testing, each hectare on the Eglin test grid received at least times more TCDD than a hectare sprayed with Agent Orange in Vietnam.

Much of the vegetation on the test site had been removed, allowing an opportunity to study ground-based residues that would not be affected by interception of the sprayed herbicides by the forest canopy Young et al.

Small but detectable levels of TCDD in the parts per trillion range were found in some soil samples 20 years after the last application of herbicide. It was estimated that the vast majority of TCDD that reached the ground had been degraded by sunlight within 24 hours of spraying and would not have persisted in the environment. In the years that followed the herbicide testing, vegetation growth gradually returned to normal, indicating that there was no persistent herbicide effect.

Examination of animal species that lived in close contact with the soil did not reveal significant health effects Young et al. In summary, very large quantities of herbicides were applied to the Eglin Air Force Base test site, far more than would be applied during typical aerial spraying, and far more that were used during the herbicide tests at CFB Gagetown June , , and June , see " How much Agent Orange was sprayed at CFB Gagetown?

These herbicides were applied over areas where vegetation had been removed, thereby maximizing the amount of herbicide that reached the ground. No long-term negative effects on vegetation or wildlife were detected. Although TCDD could be detected in the soil years after the testing, the amounts present were extremely small and did not appear to have a significant adverse effect on the environment Young et al.

Most of the TCDD released into the environment comes from combustion sources, such as municipal and medical waste incineration, backyard burning of household waste such as plastics, cement kilns, forest and brush fires, and burning of fuel for agricultural purposes and home heating. TCDD can be formed in metals operations, such as aluminum smelting, steel production and scrap metal recovery. Because of this past and continued production and release of TCDD, it is everywhere in our environment in very small quantities.

Cigarette smoke is also an important source of exposure Muto et al. A gram is a relatively small amount: A picogram is a trillionth of a gram. Put another way, one picogram is one part per trillion of a gram see "How much is a part per trillion ppt?

Every day, the average adult is exposed to about billion molecules of TCDD. In a study of industrial workers for whom an elevated cancer risk was observed see " What are the health risks associated with large exposures to TCDD? Health Canada's tolerable daily intake value is currently under review, but will likely be equivalent to the WHO value. Based on the assessment of health authorities, the tolerable daily intake is the amount of TCDD that people can be exposed to every day of their lives without harm.

The tolerable daily intake is expressed in a manner that takes into account differences in body weight between different people. For example, the tolerable daily intake of TCDD for a 70 kilogram adult is picograms 4 picograms of TCDD per kilogram multiplied by 70 kilograms per day. For a 80 kilogram adult, the tolerable daily intake would be picograms 4 picograms of TCDD per kilogram multiplied by 80 kilograms per day.

It is estimated that in North America, the average body burden of TCDD the amount of TCDD contained within our bodies is parts per trillion ppt , measured either in body fat or in blood lipids Hays et al. In comparison, the average serum level of TCDD in a sample of Ranch Hand personnel who handled and sprayed herbicides in Vietnam was 49 ppt in , many years after exposure had occurred.

Because half the TCDD in our bodies is naturally eliminated every years TCDD's half-life , it was estimated that 2 to 4 half-lives had passed since the time of their exposure and that their serum TCDD levels around the time of exposure had probably been several hundred ppt MMWR, Other Vietnam veterans who did not directly spray or handle herbicides in Vietnam had body burdens of TCDD that were no different than normal background levels, in the range of 2 to 4 ppt Young et al.

It is estimated that the maximum TCDD dose experienced by Ranch Hand veterans was only about one tenth of the maximum predicted dose of industrial workers Akhtar et al. In a study of heavily exposed industrial workers for whom evidence of associations between TCDD and cancer was observed , the average estimated serum level of TCDD at the end of exposure was ppt, with a maximum value of ppt Steenland et al.

People who have serum TCDD levels greater than ppt develop a skin condition known as chloracne Greene et al. We are all exposed to TCDD. It can be measured in our bodies. The risk of health effects associated with TCDD is entirely dependent on the degree of exposure, or dose see "Under what circumstances might Agent Orange or its ingredients lead to health effects?

During the tests, records indicate that helicopters sprayed the herbicide in an unused and remote area of the base, not in proximity to any residential or working areas, under strictly controlled conditions, and with little to no wind.

The total area sprayed by various herbicides containing 2,4,5-T eg. Agent Orange, Agent Purple, and others was The total amount of all herbicides containing 2,4,5-T that were sprayed during the and tests was kg, of which kg was Agent Orange and kg was Agent Purple AD Technical Memo , ; AD Technical Memo , The greatest amount of herbicide exposure resulting from the June , , and June , tests would likely have occurred among those people who directly handled or were sprayed by herbicides.

In considering their health risks, it is important to consider the concept of dose-response see "Under what circumstances might Agent Orange or its ingredients lead to health effects? Most of the associations between TCDD exposure and health outcomes have been observed in heavily exposed industrial workers. Vietnam veterans with the greatest amount of herbicide exposure Operation Ranch Hand veterans had less overall TCDD exposure than heavily exposed industrial workers.

Personnel exposed to herbicides during June , , and June , testing at CFB Gagetown would generally have had less exposure than Ranch Hand veterans, who on average spent more than a year in Vietnam Akhtar et al.

Without knowing specific details of how the herbicides were handled during the June , , and June , tests, subsequent activities that might have resulted in exposure, and the specific TCDD concentrations of the herbicides used, it is not possible to make definitive statements about the degree of potential exposure and health risks for particular individuals involved. Given the relatively small herbicide quantities applied, relatively brief duration of exposure, and the findings of health studies of more heavily exposed groups, the scientific evidence reviewed above suggests that the health risks would generally be lower than the risk for more heavily-exposed Vietnam veterans and lower still than the risk for the heavily-exposed industrial and agricultural workers on whom most of the Institute of Medicine associations are based.

With respect to CF members travelling through the targeted area after the spraying or conducting activities elsewhere in the training area, the evidence summarized above suggests that, in the absence of an unusual exposure incident, it is unlikely that they would have received a level of exposure significant enough to harm human health Young et al. The only study on the question of health effects of people living near CFB Gagetown was conducted in by Health and Welfare Canada and it looked at limited data and limited health information.

In order to assess if the use of Agent Orange and other herbicides had resulted in detectable health effects in the communities surrounding CFB Gagetown, Sunbury County which borders the area of CFB Gagetown where the June , , and June , herbicide testing occurred was the area chosen for study. Death rates due to all causes, circulatory diseases, and cancer were either lower or no different than expected Wigle et al. Potential reproductive health effects were evaluated by studying the outcomes of babies born around the time of spraying and in the months that followed.

The study concluded that the herbicide testing at CFB Gagetown " resulted in no significant increase of adverse pregnancy outcome events in the population adjacent to Camp Gagetown " Wigle et al. The study also noted " Based on climatic conditions, spray technique, knowledge of the chemicals used and the results of other studies it is unlikely that persons outside the confines of Camp Gagetown would have received a significant exposure to any of the defoliants tested " Wigle et al. DND is assessing what further health study may be required.

The evidence summarized above and what is currently known about the spraying suggest that it is unlikely that the herbicides sprayed at CFB Gagetown June , , and June , would have travelled a significant distance beyond the target area or resulted in sufficient environmental contamination to harm human health see "What happens to Agent Orange after it is sprayed?

Sufficiently great exposure to TCDD-containing herbicides could potentially increase the risk of illnesses associated with Agent Orange see " Under what circumstances might Agent Orange or its ingredients lead to health effects? Unfortunately, it is rare for anyone to live his or her entire life without any sort of health problem. The Public Health Agency of Canada contains a wealth of information on the burden of disease in Canada http: For example, by the middle of , more than 35 Canadians had died of cardiovascular disease and more than 30 Canadians had died of cancer http: According to Diabetes in Canada Second Edition , it is estimated that 30 Canadians die each year from diabetes and diabetes-related complications http: According to Canadian Cancer Statistics http: In other words, the average Canadian male has a 1 in 2.

It is estimated that in , out of every men in Canada and out of every women will develop cancer. Roughly Canadians will be diagnosed with cancer and 69 Canadians will die from cancer in

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