Physical information for selected naturally occurring Radionuclides 
At present time the different environmental compartments suffer from excessive accumulation of various toxic pollutants, hazardous fallout contaminants and several naturally occurring radionuclides, including potassium-40, thorium and uranium with the natural decay series of Th and U as well as several other man-made radionuclides. It is now of common practice to regulate any uncontrolled release of hazardous wastes in different environmental compartment . Toxic hazardous wastes are defined as containing chemicals posing substantial hazards to human health or to the environment when improperly treated, stored, transported, or disposed. Scientific studies show that these wastes have toxic, carcinogenic, mutagenic, or teratogenic effects on human or other life forms. The majority of hazardous waste is generated by the chemical manufacturing, petroleum, pesticides and coal processing industries. Hazardous wastes may enter the body through ingestion, inhalation, absorption, or puncture wounds .
On the other hand, nearly all the naturally occurring radioactive materials are considered in balance state. However, in several industrial processes e.g., mining of minerals (U, Th, steel, rare earth’s metals), phosphate, oil and gas production, concentration of the natural radionuclides may be altered than its physical state, and exists in concentrations over than that exists naturally.
Wastes associated with the various industrial activities, with enhanced levels of the natural radioactivity as a result of industrial process, causes what is called, “Technological Enhanced-Naturally Occurring Radioactive Materials”, to be named as acronym word ''TE-NORM''. For instance, TE-NORM scales may build up inside of oil field production tubing and may concentrate considerable quantities of radioactive material that has the potential to expose humans to relatively high dose of radioactivity. TE-NORM is often precipitated as sludge and scales. The human body cannot sense or detect TE-NORM, so, it can be detected and measured indirectly through their ionizing radiation using specialized instrumentation . Uncontrolled release of activities associated with enhanced levels of NORM can contaminate the environment and pose a risk to human health. These risks can be alleviated by the adoption of controls to identify where NORM is present; and by the control of NORM-contaminated equipment and waste while protecting workers.
1.1. Discovery TE-NORM in industry
The history of TE-NORM in oil and gas production follows closely in history of the discovery of radioactivity in the first part of 20th century. We must remember that, the discovery of radioactivity is more than one hundred years old. In 1918, a Canadian paper was published on radioactivity in natural gases. In the 1930's an elevated radium level were detected in the Russian oilfields. In 1953, the US geological society published a paper on uranium and helium in gas formations. In 1973, (EPA) performed a study on the presence Rn-222 natural gases [5-8].
A number of major oil companies helped sponsor a study on radon in natural gas products that was completed in 1975. The thrust of this study was the potential effect that radon would have on the consumer of natural gas products. Radon contamination of natural gas has been known for nearly 100 years . These studies concluded that, radon in natural gas products does not present any hazard to the consumer. However, that radon could be a problem for different processing industries and some research efforts have focused on this concern [9-10].
In 1981, scale produced on offshore oil platforms in the North Sea was found to contain TE-NORM in significant quantities. These findings were presented in a 1985 offshore technology conference paper on radioactive scale formation in Houston, Texas, USA. Consequently, industry and government officials were aware of the possibility that TE-NORM scale could be present in US domestic operations. In 1986, significant TE-NORM scale was found in Laurel, Mississippi (USA). Some rather alarming press headlines and featured articles followed shortly in both Mississippi and Louisiana after the presence of TE-NORM in the oil path became better known. These articles stressed the fact that there are no current regulations, either by USA or other federal governments controlling this radioactive waste and called for their creation and enforcement. Since TE-NORM was first re-discovered domestically, the oil and gas industry has responded progressively to TE-NORM issues by notifying appropriate state agencies, initiating field surveys and studies to characterize and locate occurrence of TE-NORM in conjunction with the American Petroleum Institute, informing other oil and gas operations, employees and contractors, and reviewing operating practices .
TE-NORM contamination of oil and gas industry petroleum equipment has been identified world- wide, e.g. USA (Alaska, Gulf of Mexico region), the North Sea region, Canada, Australia, several Middle East countries (Egypt, Saudi Arabia...etc.). Since 1918 till 1980, most researches were focused on the TE-NORM contamination of natural gas facilities, and the contamination is attributed to 226Ra as well as 222Rn gas and its decay products, e.g. 218Po, 214Pb, 214Bi, and 210Pb. Within the text, the activity concentration ranges from background level to several hundreds Bq/g (226Ra). Doses to workers involved in handling, contaminated equipment, or waste are usually very low, and the main problem related to radioactive deposits is waste disposal . The presence of TE-NORM or naturally occurring radionuclides in the product materials from oil and gas facilities, give rise to deposits with enhanced levels of these radionuclides in the processing equipment .
1.2. Origin and formation of TE-NORM
In nature, there are three naturally occurring radioactive decay series. The first series, known as thorium series, consists of a group of radionuclides related through decay in which all the mass numbers are evenly divisible by the number four, (4n) series. This series has its origin radionuclides Th-232, its abundance is 100%, specific activity is 2.4 × 105 dpm/g, which undergoes α -decay with a half-life of 1.41 × 1010 y. The terminal nuclide in this decay series is the stable Pb-208. In this series, the transformation from the original parent Th-232 to the finial product Pb-208 requires 7α and 4β -decays. The long-lived intermediate is 6.7 y for Ra-228, Fig. (1).
The second series is the uranium series, which consists of group radionuclides that, the parent radionuclide in this series is U-238 (4n+2) abundance = 99.27 %, which undergoes α -decay with a half-life of 4.47 × 109 y. The stable product of the uranium series is Pb-206, which is reached after 8α and 6β -decay steps, Fig. (2). This is a particularly important series in nature since it provides the more important isotopes of elements Ra, Rn and Po, which can be isolated in large amounts in the processing of uranium minerals. Each ton of uranium is associated with 0.34 g of Ra-226.
The third radioactive decay series, (4n+3) known as the actinium series, the head of this series is U-235, which has an abundance of 0.72 % and a half-life of 7.1 × 108 y for α -decay. The stable end product of this series is Pb-207, which is formed after 7α and 4β -decay steps. The specific activity of U-235 is 4.8 × 106 dpm/g, Fig. (3) .
Other important radionuclide that exists in the nature is potasium-40 (t1/2. 1.28 × 109 y, isotopic abundance 0.0118 %). K-40 is found in plants, animals and in human bones. It is widely distributed in nature with volume concentrations ranging from 0.1 to 3.5 % in carbonates (limestones). The bones of an average human body contain concentrations of ~ 17 mg of K-40. The average radiation dose received from K-40 is 0.25 mSv/y to tissue and ~ 0.36 mSv/y to bone.
Radioactive materials such as uranium and thorium were incorporated in the Earth’s crust when it was formed; these normally exist at low concentrations in rock formations. Decay of these unstable radioactive elements produces other radionuclides that, under certain conditions (dependent upon pressure, temperature, acidity
The TE-NORM waste occurs though the extraction and treatment of liquid and gases hydrocarbons and is generally accompanied by the formation and accumulation of radioactive scales, sludges and films. The petroleum waste (scale or sludge) was produced by two mechanisms either incorporate or precipitate into the production equipment such as pipelines, tank storage, pumps etc. The TE-NORM waste as scale and sludge generated in oil and gas equipments is due to the precipitation of alkaline earth metals as sulphates, carbonates, and/or silicates .
Some investigations were performed concerning the composition and characterization of the formed radioactive TE-NORM waste produced during oil and gas processing. Nuclear spectroscopic analysis showed that, the main radionuclides present in these wastes are traces of 238U and 232Th as well as their decay daughters. These studies indicated that the incorporation and co-precipitation of these natural radionuclides with alkaline earth metals (e.g., Mg, Ca, Sr, Ba) and some quantities of lead as sulphates, carbonates and/or silicates . Some other studies were also performed under controlled production conditions, proved that, the factors that are greatly responsible for the formation of radioactive scale and/or sludge are water composition. The way in which the scales are deposited is connected to the pipes, superficial features, fluid-dynamic phenomena and crystallization kinetics. Testa et al. found that, variations in sulphates and carbonate solubility can give rise to scale formation, which are connected to some physical and chemical factors, e.g., temperature variation, pressure changes, pH-balance, evaporation in the gas extraction pipes and injection of incompatible sea waters. Also, the re-injected water into the reservoirs to maintain the production pressure during the field exploration seemed to be a principal cause for the scale formation . As a consequence of the physical and chemical processes during the extraction of oil, besides the production water additional scale is obtained. Scale production in gas and oil field equipment is due to precipitation of alkaline earth metal sulphates or carbonates according to the following chemical reactions:
Therefore, the observed levels of activity concentrations both in the separated sludge and solid scale are much higher than those observed in the produced water from the oil industry. Many of the physical characteristics of oil formations, high temperature pressure,..etc. tends to increase the radionuclide solubility in production fluids. This due to the complex process for sludge formation. Generally, uranium and thorium are relatively insoluble and remain stationary in the reservoir, while, radium is more soluble and may become mobilized in the produced water phase of the reservoir. It has been estimated that: 25000 tones of TE-NORM contaminated scale, and 225000 tones of TE-NORM contaminated sludge, are generated each year by the petroleum industry. The available data indicate that, the total radium levels to extreme measurements of 15.17 kBq/g scale and 25.9 kBq/g in sludge .
Many industries produce wastes that might contain natural radionuclides. Some of industries producing TE-NORM are coal, petroleum and natural gas, tungsten, phosphate fertilizer production, mineral processing, zirconium minerals or sand, welding and ceramics and building materials industry. In this review, we are interested in petroleum and phosphate industries that are the important industries in Egypt.
1.3. Characterization and radiological assessment
Some analytical and radiometric techniques are used to identify the chemical composition and radioactivity level of samples. The main phase composition of samples has been carried out using a powder X -ray diffractormeter equipped with a copper target and a nickel filter. The micro and trace-elemental analysis of samples have been performed by X -ray fluorescence (XRF) spectrometer. The IR spectra of the samples under study were done using FT-IR spectrometer. The different naturally occurring radionuclides present in the tested samples, were identified and the concentration of their radioactivity levels were detected and determined using a typical non-destructive nuclear spectroscopic technique. This has been performed using γ -ray spectrometer equipped with a High Purity Germanium (HPGe) detector.
A : is the specific activity of the parent radionuclide or its daughters assuming the secular equilibrium in the test sample (Bq/kg or Bq/L),
Ci,e: is the net count of radionuclide (i) at γ -energy line (e) in keV,
εi,e : is the absolute efficiency of the used γ -ray spectrometer,
Pγ i,e: is the photopeak intensity (%),
G : is the geometry factor which is equal to unity when all test samples were counted under the same conditions,
m : is the weight of constant sample (kg) and
t : is the counting time in seconds.
Evaluation of the radiological characteristics, the parameters that are determined include radon emanation fraction released (EF), radium equivalent index (Ra-eq) and total absorbed dose rate (Dγr) for the test samples.
To determine the radon (222Rn) emanation fraction released (EF), the waste samples were initially counted (C1) for 2 h after sealing the sample container, and counted again (C2) after reaching the radioactive equilibrium between 222Rn decayed from 226Ra and its respective short-life daughters. The 222Rn EC was determined using the formula [20,21]:
Where 222Rn EF is the radon emanation fraction; A0 is the amount (net count rate, cps) of 222Rn existing at the sealing time of the sample container; N is the amount of (net count rate, cps) of 222Rn emanated at the radioactive equilibrium.
To represent the activity levels of the materials containing 226Ra, 232Th and 40K, by a single quantity, which takes into account the radiation hazards associated with them, a common radiological index has been introduced. This index is called radium equivalent (Ra-eq) activity and is mathematically calculated according to the following formula [22,23]:
Where: ARa, ATh and AK are the activities (Bq/kg) of 226Ra (238U-series), 232Th and 40K, respectively.
The absorbed dose rates (Dγr) due to γ -radiations in air at 1m above the ground surface for the uniform distribution of the naturally occurring radionuclides (226Ra, 232Th and 40K) were calculated based on guidelines provided by UNSCEAR [24,25]. Therefore, Dγr in outdoor air at 1 m above the ground was calculated as follows:
2. TE-NORM in petroleum industry
In this part, the waste generated from oil and gas production that were investigated in Egypt and other countries are reviewed. The waste samples namely, Scales, sludge and produced water have been characterized.
2.1. TE-NORM in scales and sludge
The activity concentration of 226Ra in the TE-NORM waste at three different sites for petroleum and gas production in Egypt has been determined using gamma spectroscopy. El Afifi et al.  chose three sites of oil and gas production for radiological assessment; (1) in the South Sinai Governorate, (2) in the Suez Gulf area, (3) in the Matrouh Governorate. Seven waste samples with an intermediate structure (mixed between granular and massive) were taken from Abu Rudeis (AR) onshore oil and gas field in the Suez Gulf. Nine samples representing two waste types were from Gabal El Zeit (GEZ) offshore oil and gas field at the Suez Gulf. Four samples had a granular structure and 5 samples had a massive one. Eighteen samples with granular structure were taken from Badr El Din (BED) offshore oil and gas field, respectively (Fig. 4). The TE-NORM waste samples taken for analysis, are a mix of scale and sludge formed in the production equipment and removed during the periodical maintenance. The samples were taken from the TE-NORM waste stacks accumulated around the petroleum and gas plants using a stainless steel template of 25×25 cm2 with a thickness of 5 cm.
The results showed that the average activity concentrations of 226Ra changed between 5.9 and 68.9 kBq/kg (dry weight) in the waste samples from GEZ and AR fields, respectively. In Gabal El Zeit field (GEZ), granular and massive wastes were investigated. The lower activity concentrations (28.6 kBq/kg) of 226R were found in granular samples (GS), while higher values (56.6 kBq/kg) were found in the massive samples (MS). The activity concentrations of 226Ra in all investigated waste samples from different region in Egypt can be ordered as follows: AR > BED > GEZ.
The mean activity concentrations of 232Th were 25.4, 2.6, 7.2 and 61.3 kBq/kg and those of 40K were 1.3, 0.96, 2.3 and 5.9 kBq/kg, for AR, GEZ (GS), GEZ(MS), and BED TE-NORM waste samples, respectively . The lower 226Ra activity concentration in the waste samples may be due to the lower Ra content in the subsurface formation. Therefore, the quantity of 226Ra leached by oil and gas during exploration was lower in this case. Generally, the variation in the 226Ra activity concentrations in TENORM wastes of different origins, can attributed to the differences in the Ra/Ba ratio in the formation waters scale and/or sludge formation processes on the exterior surfaces of the casing material and the amount of 226Ra in the subsurface . The Ra content depends on the amount of Ra present in subsurface formation, formation water chemistry, extraction and treatment processes and the age of the waste after production.
The average 222Rn emanation fraction released from the TE-NORM wastes investigated ranged from 0.053 to 0.081 in the massive samples (MS) from GEZ field and the granular samples (GS) from BED field, respectively. The 222Rn EF released from MS is lower than that of GS although the activity concentration of 226Ra in the MS is higher. The variation of EF is independent of the 226Ra content and is strongly correlated to the grain surface density [7,8,19]. The smaller the grain size the higher the EF .
The main types of scale encountered in oil & gas facilities are sulphate scale which results from drilling clay, it called Barite slurry. It is usually colorless or milky white, but can be almost any color, depending on the impurities trapped in the crystals during their formation. Barite is relatively soft, measuring 3-3.5 on Mohs' scale of hardness. It is unusually heavy for a non-metallic mineral. The high density is responsible for its value in many applications. Barite slurry is generally used as mud in drilling oil. Barite is chemically inert and insoluble. Radium is chemically similar to barium (Ba), strontium (Sr) and calcium (Ca), hence radium co-precipitates with Sr, Ba or Ca scale forming radium sulphate, radium carbonate and – in some cases – radium silicate. The mixing of seawater, which is rich in sulphate, with the formation water, which is rich in brine, increases the scaling formation tendency. Also the sudden change in pressure and temperature or even acidity of the formation water, as it is brought to the surface, contributes to scale build-up. This phenomenon has significant implications for the production of oil; in this case the capacity of the pipe to transfer oil would be reduced significantly. The activity concentration of 226Ra and 228Ra in hard scales in Egypt and some other countries are mentioned in Table 2.
El Afifi and Awwad  characterized TE-NORM from Abu Rudeis region (onshore oil field, Suez gulf area) in the North Sinai Governorate, Egypt. The mineralogical analysis by X-ray techniques (XRF and XRD) has been carried out. Table 3 represents the chemical analysis of the TE-NORM waste samples using the XRF technique. The data showed major elements (Si, Fe, Al and Na) and alkaline earth elements (Mg, Ca, Sr and Ba) .
The radioactivity of naturally occurring radionuclides of 238U, 235U, 232Th-series and 40K in the sediment samples of the TE-NORM waste from Abu Rudeis region before fractionation (B.F.) and after fractionation (A.F.) are given in Table 4. The bulk waste was fractionated into nine homogeneous fractions with different particle sizes (< 3.0– < 0.1 mm) to show the effect of particle size on the activity distribution. Moreover, radiation hazardous indices including the radium equivalent activity (Ra-eq), radon (222Rn) emanation coefficient (EC) and absorbed dose rate (Dγr) were also estimated of TE-NORM waste. The radon emanation coefficient (EC) is a very important radiological index used to evaluate the amount of the 222Rn emanated fraction released from the waste materials containing naturally occurring radionuclides (e.g. 238U, 235U and 226Ra). In this study, the assessment of Rn EC is related only to 222Rn decayed from its parent 226Ra content in the waste. Since 222Rn and its respective decay progenies (e.g. 210Pb and 210Po) have longer half lives than that of other radon isotopes, 222Rn is considered to be more radiological hazardous to human health than radionuclides coming from other radon isotopes. Fig. 5 represents the 222Rn EC released from the bulk TE-NORM waste and the different fractions. The amount of the 222Rn fraction emanated from the bulk waste was 0.066. It is found that the grain size has an effect on the amount of 222Rn EC. There is a gradual increase in the 222Rn EC with the waste particle size. This was observed in fine particle sizes from less than 0.1 mm up to 2 mm. In this range, 222Rn EC increased from 0.041 to 0.086. There is no effect of the waste particle sizes on the 222Rn EC released from large particle sizes as shown in the grain sizes between 2 and 3 mm. The radon EC found in this range of particle sizes was ranging between 0.093 and 0.095 .
Reported levels of the 226Ra and 228Ra activity concentrations observed in the solid scale and sludge in different countries are listed in Table 5.
The radium equivalent activity (Ra-eq) is a radiation index, used to evaluate the actual radioactivity in the materials containing naturally occurring radionuclides, e.g. 238U and 232Th series, and/or 40K. Values of Ra-eq activity for the bulk TENORM waste and the waste fractions were calculated. It is clear that Ra-eq exceeds the maximum permissible radium activity (Ref. value is 370 Bq/kg) as reported by Zaidi et al. . The higher Ra-eq activity reached about 164.9 kBq/kg in fraction F8, whilst the lower value amounted 70.4 kBq/kg in F2 (Fig. 6). The higher the radioactivity level in the waste, the higher is the radiological impacts, especially when considering the potential of operators to be exposed via internal contamination by ingesting the dust during waste processing. The total absorbed dose rate due to g-emissions was estimated and the obtained values are presented in Fig. 6 . It is recommended that the acceptable total absorbed dose rate by the workers in areas containing g-radiations from 238U and 232Th series and their respective decay progenies, as well as 40K, must not exceed 0.055 mGy/h . It is obvious that the calculated total absorbed dose rates for all waste samples are higher than the recommended dose level that are acceptable (Fig. 8). The low total absorbed g-dose rate is 31 mGy/h in fraction F2, while the high value is 72.7 mGy/h in fraction F8. It is clear that the absorbed dose rate depends on the activities of g-emitters (e.g. 226Ra, 232Th 40K), while it is independent of the waste particle size. Therefore, the total absorbed dose rates increases with the activity concentration, and consequently enhances the radiological impact on the workers surrounded by the wastes.
As shown in Table 5, the concentration levels of radium nuclides in scale vary within a wide range being much higher than those of the sludge. According to the latest Environmental Protection Agency (EPA) estimation, the average radium nuclide concentration is around 18,000 Bq/kg and 2800 Bq/kg in scale and sludge, respectively . Elevated concentration activities of both radionuclides, exceeding the exemption level of 10,000 Bq/kg recommended by IAEA safety standards, were frequently found in the scale samples. A large uncertainty is observed in the estimations of the total amount of radioactive waste generated by oil industry, and the EPA assumes that 100 tons of scale per oil well are generated annually in the United States , while for the North Sea wells a somewhat lower value of 20 t is suggested  and only 2.25 t per year by one oil-producing well for Latin American oil producing countries . It was also estimated that approximately 2.5 × 104 and 2.25 × 105 tons of contaminated scale and sludge, respectively, were generated each year from the petroleum industry in the middle of the previous decade [47,48]. This means that TENORM waste from the oil industry may generate radiation exposure levels which require attention and continuous monitoring during some routine operation in this industry. This exposure is caused by external radiation coming from the 226Ra radionuclide and its progenies: 214Pb and 214Bi as well as by inhalation of α -emitting radionuclides: 222Rn as well as 218Po and 214 Po formed from 222Rn escaping into the air adjacent to scale deposits, as reported in Table 6.
2.2. TE-NORM in produced water
Oil and gas reservoirs contain water (formation water) that becomes produced water when brought to the surface during hydrocarbon production. Oil reservoirs can contain large volumes of this water whereas gas reservoirs typically produce smaller quantities. In many fields, water is injected into the reservoir to maintain pressure and / or maximize production. In many offshore oil fields sea water is additionally injected to maintain pressure, and it mixes with the formation water. In such cases, in the exploited oil/water mixture, the content of the production water can reach even 95%. For this reason, the produced waters are typically saline and rich in Cl– anions forming aqueous complexes with Ra that enhance the mobility of Ra nuclides from adjacent geological rocks into these waters . Comprehensive older literature reviews of radium nuclide concentrations in formation and produced water indicated an average radium nuclide concentration in waters in excess of 1.85 Bq/dm3 and exceptionally up to ~ 1000 Bq/dm3 [49,51,52]. As 226Ra originated from the radioactive decay of 238U, while 228Ra from 232Th, the 226Ra/228Ra ratio in the oil-field brines depends on the U/Th ratio of the reservoir rock and ranges from 0.1 to 2.0, but for the most cases its activities are comparable.
Typical ranges or average values of the radium radionuclide concentrations in the formation or produced water from different oil fields, including the recent data, are listed in Table 7 [29,32,34,38,51,53-62].
A critical review of the intense studies of the activity concentrations of 226Ra, 228Ra as well as 210Pb and 210Po in produced water in 2003 from Norwegian oil and gas platforms located in the North Sea were also reported . The concentrations of 226Ra and 228Ra in produced water discharged from these offshore platforms vary between 0.1 Bq/dm3 and about 200 Bq/dm3 with the average values estimated to be 3.3 Bq/dm3 and 2.8 Bq/dm3, respectively. Slightly higher radium activities ~ 10 Bq/dm3 have been found for produced water outfalls in the Gulf of Mexico . The European Commission (EC) derived the specific clearance levels at low activity for metals and buildings in radiation protection. The world wide average concentration of these radionuclides in produced water discharged to the environment is estimated at 10 Bq/l. These concentrations are approximately three orders of magnitude higher than natural concentrations of radium in drinking or sea water. Because the radium radionuclide concentrations in that waste water are usually below the clearance levels (Table 8), it is recognized as a low specific activity waste and they may be injected into underground formations or disposed into the sea.
A comprehensive evaluation of discharges from the oil industry to the sea was done for European waters during the European Commission Marina Project .
The annual release of 226Ra and 228Ra with produced water from off-shore fields in Europe in the 1990s stabilized at around 5 and 2.5 TBq per year, respectively. The commonly used two steps model of the radionuclide dispersing and diluting in the water in the vicinity of the oil platforms predicts a diluting factor up to 103 within minutes and within a few meters of the discharge source . Therefore, additional radium nuclide concentrations in seawater of the local zone could be estimated as equal to around 5–10 Bq/m3, in comparison with the natural concentration of around 1 Bq/m3 for 226Ra. The radium activities in the produced water for the North Sea, a yearly release of 0.65 TBq for 226Ra and 0.33 TBq for 228Ra was appraised for offshore oil production from Argentina and Brazil .
Produced water contains a complex mixture of inorganic (dissolved salts, trace metals, suspended particles) and organic (dispersed and dissolved hydrocarbons, organic acids) compounds, and in many cases, residual chemical additives (e.g. scale and corrosion inhibitors) that are added into the hydrocarbon production process. Feasible alternatives for the management and disposal of produced water should be evaluated and integrated into production design. These alternatives may include injection along with seawater for reservoir pressure maintenance, injection into a suitable offshore disposal well, or export to shore with produced hydrocarbons for treatment and disposal. If none of these alternatives are technically or financially feasible, produced water should be treated before disposal into the marine environment. Treatment technologies to consider include combinations of gravity and / or mechanical separation and chemical treatment, and may include a multistage system, typically including a skim tank or a parallel plate separator, followed by a gas flotation cell or hydrocyclone. There are also a number of treatment package technologies available that should be considered depending on the application and particular field conditions. Sufficient treatment system backup capability should be in place to ensure continual operation and for use in the event of failure of an alternative disposal method, for example, produced water injection system failure. Where disposal to sea is necessary, all means to reduce the volume of produced water should be considered, including:
Adequate well management during well completion activities to minimize water production;
Recompletion of high water producing wells to minimize water production;
Use of down hole fluid separation techniques, where possible, and water shutoff techniques, when technically and economically feasible;
Shutting in high water producing wells. To minimize environmental hazards related to residual chemical additives in the produced water stream, where surface disposal methods are used, production chemicals should be selected carefully by taking into account their volume, toxicity, bioavailability, and bioaccumulation potential .
The average worldwide activity levels of uranium (U), thorium (Th) and potassium (K)  and the exemption activity levels of NORM as recommended in the IAEA basic safety standards , were given at Tables 9&10. The average worldwide levels of the most common radiological indices  was given at Table 11. These indices include radium equivalent (Ra-eq), total absorbed dose (Dγr) and effective annual dose rate (EDAR).
2.3. Investigation of TE-NORM treatment in petroleum industry
In the last decade, attention was focused on the environmental and health impacts from the uncontrolled release of TENORM wastes [19,28,70,71]. Therefore, the treatment of these wastes is of increasing interest because accumulation of large amounts with a significant activity may cause a health risks to the workers through exposure, inhalation of radon (222Rn) decayed from radium and/or ingestion of waste dust during the periodical maintenance of the equipment used. The trials towards the treatment of TENORM wastes from many industries are still limited. In this concern, removal of 226Ra from TENORM wastes produced from oil and gas industry was carried out by a simple extraction process using saline solutions (i.e., seawater) and chemical solutions . The chemical treatment process of TE-NORM sludge has been carried out by suspending the clay fraction content in the solid waste in suitable leaching solutions was reported. It was found that, the maximum removal % of 226Ra is ~ 85% 
El-Afifi, studied the treatment of radioactive waste containing 226Ra from oil and gas production, using different chemical solutions, in terms of a simple and sequential techniques based on suspending 226Ra through the clay fraction in the waste. More than 50% of 226Ra was removed through the treatment using moderate acids and salts solutions, while more than, 75% of 226Ra was removed based on successive treatment or using some strong chelating reagent solutions .
The development of the treatment of a sludge TENORM waste produced from the petroleum industry in Egypt, using selective leaching solutions based on two approaches ‘A’ and ‘B’ has been investigated by El-Afifi et al. . The results obtained showed that treatment of the waste through main four successive leaching steps removed ~ 78 and 91% of 226Ra, 65 and 87% of 228Ra as well as 76 and ~ 90% of 224Ra using approaches A and B, respectively . El-Afifi et al.  reported some data about the radiological characterization for phosphogypsum waste and phosphate rocke samples by γ -ray spectrometer. El-Didamony et al. used the solvent extraction technique in treatment of phosphogypsum waste obtained as a byproduct of phosphoric acid production from phosphate ore.
The naturally occurring radioactive materials (NORM) are found everywhere. We are exposed to it every day. NORM represent an integral part of the planet, our bodies, the food we eat, air we breath, the places where we live and work, and within products we use. However, in the exploration and extraction processes of oil and gas, the natural radionuclides 238U, 235U and 232Th, as well as the radium-radionuclides (223Ra, 224Ra, 226Ra and 228Ra) and 210Pb,.etc., are brought to the slurry surfaces and may contain levels of radioactivity above the surface background. The petroleum waste (scale or sludge) have been produced by two mechanisms: either incorporation or precipitation onto the production equipment such as: pipelines, tank storage, pumps,..etc. The waste generated in oil and gas equipment is due to the precipitation of alkaline earth metals as sulfate, carbonates and/or silicates. It is clear that PG and sludge and scale wastes represent one of the major sources of 226Ra in the environment. Since the concentration of 226Ra found in both of them waste exceeds that permitted by the international regulations, it was found necessary to reduce the risks due to indoor radon and direct γ -radiation in each wastes to be used in different life aspects.
Nomenclature of symbols associated with this article is listed as follows.