Several constituents have been described as emerging pollutants originating from pharmaceuticals and personal care products (PPCPs), which found their way into the environment through human and animal excretion (urine and feces) disposal in wastewater. The disposal of pharmaceuticals in water ultimately results in micro contamination of the environment from nanogram-per-liter (ng/L) to microgram-per-liter (µg/L), which only became detectable by the recent improvements in instrumental methods (Ahuja, 2019; Cuong et al., 2011; Bell et al., 2011). Despite much progress and innovation in wastewater treatment technologies, pharmaceuticals continue to be detected in surface water and ultimately in our drinking water and beverages. The concentration of pharmaceuticals in surface water ranges from several to over a hundred ng/dm3 (Brünjes and Hofmann, 2020; Szymonik et al., 2017). Emission of Gd compounds from contrast-enhanced MRI imaging has been the principal source of anthropogenic Gd anomalies in surface water. The GBCAs administered during magnetic resonance imaging (MRI) end up directly in coastal seawaters primarily through excretion from the patient's urine or hospital sewage disposals. Ideally, approximately 91 minutes is required to excrete GBCAS from a patient with healthy kidney function; however, it may take longer for a patient suffering from renal impairment. Increased Gd concentrations in water from rural areas with no MRI facilities have been attributed to many outpatients receiving MRI scans and returning home to release the Gd through their renal route (Atinkpahoun et al., 2020). The increasing Gd concentrations found in water systems and drinking water are of profound interest to both experts, policy makers, and the general public (Brünjes & Hofmann, 2020).
Unfortunately, conventional and advanced wastewater treatment plants' treated water is still rich in highly stable Gd due to lack of / incomplete removal (Steinberg et al., 2020; Rogowska et al., 2018; Cyris et al., 2013). A detailed study conducted by Lena Telgmann and co-researchers in 2012 has shown that approximately ninety percent of Gd are retained post-conventional wastewater treatment (Telgmann et al., 2012; Rogowska et al.,,,2018; Elizalde-González et al., 2017). Worse still, while city water treatments are not tailored to remove GBCAS, it is pertinent to note that specific GBCAS are susceptible to degradation during the treatment processes of chemical coagulation (using FeCl3 and Al2(SO4)3, which forms an acidic microenvironment). Other processes that can cause GBCAS degradation include chlorination and U.V-photolysis. (Kulaksiz and Bau, 2011a; Brünjes and Hofmann, 2020; Lee et al., 2014). Transmetallation of GBCAS involves the substitution of Gd3+ from GBCA complexes by other substituents metal ions such as Iron (Fe3+), zinc (Zn2+), and copper (Cu2+) due to their similar and, in some cases, higher thermodynamic stability, which increases the toxicity of GBCAs by releasing toxic-free Gd3+ (Lee et al., 2014). It has been shown that Gd3+ can be partially moved from chelates by competing with other metals such as magnesium and calcium when waste effluents mix up with seawater. In addition, there is evidence that zinc, calcium, and iron can partially displace Gd3+ of its medical chelating agents in vivo in spite of very high stability constants. Consequently, the environmental chemistry of Gd3+ can be determined by the abundance of inorganic and organic ligand substitutes, which also determines its bio-availability and toxicity. (Steinberg et al., 2020; Tovar-Sanchez et al., 2018; Port et al., 2008a).
GBCAs are unintentionally destabilized during conventional or advanced water treatment yielding to rapid transmetallation of GBCAS into free toxic Gd. Consequently, there is an urgent need to recover the controversial anomaly Gd during the water and wastewater treatment process to prevent the inadvertent consumption of Gd through drinking water, beverages, and other processed or raw foods.
The long environmental half-lives and high stability of the GBCAs administered during MRI examinations leave the sewage treatment process almost unchanged (Kulaksiz and Bau, 2011a McDonald et al., 2018; Thomsen, 2017; Kulaksiz, 2012; Kulaksiz and Bau, 2011b). The previous assumptions concerning the stability of GBCAs no longer hold. Recent reports show that they degrade, and their degraded products (Gd3+) are severe threats to aquatic organisms and human beings (Brünjes and Hofmann, 2020; Ebrahimi and Barbieri, 2019). Admittedly, their degradation processes and potential health impacts remain the subject of scientific debate because of the limited number of in-depth studies. Similarly, at present, the amount of anthropogenic Gd detected in tap and surface water is relatively small, ranging from 100 to 1100 ng L–1, which makes some opines that the ingestion and retention of such a low quantity of gadolinium as observed in brains seems more of a curiosity than a health concern. (Fox-Rawlings and Zuckerman, 2019; Garcia et al., 2017). However, the latter author admitted that the long-term sequestration of any toxic metal, even in an inert state, in a sensitive structure such as the brain, is perturbing. They also feared that there could be a point in its lifespan where pathological or other processes could release gadolinium and pose a risk for the local deposition concentration of gadolinium to reach either pathological levels or directly cause harm to human organs (e.g., vascular emboli). In the same vein, the potential harm of continual exposure to low levels of Gd contaminated water, particularly at critical developmental stages and for the more sensitive populace such as pregnant women and their fetuses, remained unknown (Fox-Rawlings and Zuckerman, 2019; Sherry et al., 2009). It is, however, known that fetuses and children are yet to fully develop a blood-encephalic barrier necessary to protect the passage of toxic chemicals from blood to neural tissue. Therefore, this vulnerable group of people cannot be considered safe even at the reported low-level concentration coupled with the unanimously predicted increasing deposition of Gd in the hydrosphere
Despite the emerging concerns about its toxicity, increasing Gd deposit in water from magnetic resonance imaging (MRI) examinations and radiology practices are expected (Thomsen, 2011; Thomsen et al., 2007; Rogosnitzky and Branch, 2016). This projection is reinforced by the current improvement in medical facilities worldwide due to the sudden health complications arising from the CONVID' 19 Pandemic, which probably includes installing MRI facilities either as a new supply or replacing old ones. Similarly, the number of MRI examinations performed in the USA within fifteen years (2000-2015) was more than doubled, while in Turkey, where MRI prescriptions are considered overuse, the number of MRI examinations has tripled within an interval of eight years (2008-2015; OECD, 2017). Therefore, except if the more rational use of MRI (for only essential diagnostic tests) is promoted and sustained, higher anthropogenic Gd concentrations in water resources are likely to occur as a result of an increase in applications (Brünjes and Hofmann, 2020; Caravan et al., 1999; Ebrahimi and Barbieri, 2019).
Many researchers have reported and restricted high positive Gd (Gdant) anomalies in the REE model in surface waters to the highly populated and industrialized areas with a sophisticated medical system. A typical example is a case reported for the highly populated Lorraine's northern region in France, where most contrast-enhanced MRIs are carried out (Parant et al., 2018). However, some of the publications reviewed in this paper have reported anomaly gadolinium in river water, seawater, groundwater, and tap water in developed cities and less populated locations without developed health facilities, as presented in Table 3. The number of MRI examinations per million population between 2017 and 2019 in selected countries as reported by the Organization of Economic Co-operation and Development (OECD) (OECD, 2020) are presented in Table 3. The number of MRI applications expectedly contributed to the discharge of Gd in water and the number of affected localities. Japan, Germany, the U.S., Korea, Finland, Italy, France, Australia, and Belgium have the highest number of MRI examinations in descending order expectedly; they all reported anomaly Gd in their water systems. Curiously, other countries with a relatively higher number of MRI examinations per capita have not reported any Gd case in their aquatic systems. In contrast, those with fewer MRI applications showed positive results for anomaly Gd. Thus, while anomaly Gd in the aquatic system may be directly related to the increased number of MRI devices in use, other factors such as patient migration and non-point source contamination through water tributaries could also play a significant role in its ecological distribution.
Several researchers have reported positive Gd abnormalities in several countries; hence, the problem cannot be categorized as a localized phenomenon or restricted to highly industrialized countries only (Braun et al., 2018; Kulaksiz and Bau, 2011a). For example, the value of anthropogenic Gd concentrations in wastewater effluents observed in southeast Queensland ranged from 0.1 to 1.5 nmol/kg anthropogenic Gd. However, a far greater value of 7 nmol/kg was reported in Berlin, Germany. The latter value indicates a 2000 times higher concentration than the natural concentration of Gd in the environment (GdNatural), while the former value indicates a 10–100 times more than the Natural Gd (Michael G. Lawrence, 2010), and Table 2 summarizes the geographies' spread of anomaly Gd in aquatic systems and sediments reported within the last two decades from all the six regions and across different localities except the Middle East. The positive anomalies spread of Gd in the aquatic space are anthropogenic and are more likely to be attributable to magnetic resonance imaging (MRI) (Bau & Dulski, 1996)
Table 2.
Anthropogenic Gds in water from various geographic regions and MRI Examinations per million population within the review period.
Country
|
Region
|
MRI/mill.
|
Locality
|
Water source
|
Ref.
|
|
|
|
|
|
|
|
|
Australia
|
Oceania
|
14.78
|
Moreton Bay, Mackay, Central Queensland, Brisbane River plume, Southeast Queensland
|
Wastewater, Rivers
|
(Catherine et al., 2020), (Michael G. Lawrence, 2010);(Michael Glen Lawrence & Bariel, 2010),(Rapp, 2018),(Michael G. Lawrence et al., 2009)
|
Brazil
|
America
|
N/A
|
Paranoa, Brasilia, Atibaia River and Anhumas Creek, Bahia, Salvador
|
Lake, River, Atlantic Coast Waters
|
(Pedreira et al., 2018);(Amorim et al., 2019),(de Campos & Enzweiler, 2016)
|
Turkey
|
Asia
|
11.24
|
Ankara,
|
Stream
|
(Alkan et al., 2020)
|
|
Germany
|
Europe
|
34.71
|
Halle, Rhine River, Berlin, Essen, Munich, Dresden, Karlsruhe and Düsseldorf, Berlin, North Sea
|
River, Surface water, Wastewater, Seawater, Tap water, soft drinks, and Groundwater
|
(Kulaksiz & Bau, 2011a);(Tepe et al., 2014); (Kulaksiz, 2012),(Merschel & Bau, 2015),(K. Schmidt et al., 2019),
|
Finland
|
Europe
|
28.82
|
Northern Finland
|
Sediment
|
(Hölttä, P., Nenonen, K. & Eerola, 2017)
|
|
China
|
Asia
|
N/A
|
Jinzhong, Yangtze, Sunhuajing, Pearl, Haihe River, Huaihe River, and Liaohe river. Redang Island
|
Streams, River water, Coastal water Stream Sediments
|
(J. Zhang et al., 2019)
|
|
S / Korea
|
Asia
|
30.8
|
Shihwa, Han
|
Lake and Stream
|
(I. Kim et al., 2020a),(Song et al., 2017), (Casey, 2017),(I. Kim et al., 2020b),
|
Kazakhstan
|
Asia
|
N/A
|
Aral Sea (SAS), Syr Darya River
|
Sea and River
|
(Rzymski et al., 2019)
|
|
Malaysia
|
Asia
|
N/A
|
Linggi
|
River and Lake
|
(Elias et al., 2019)
|
|
USA
|
America
|
40.44
|
San Francisco, Erie, Ohio, Pennsylvania, Beaver, Allegheny, Mississippi, Monongahela, Juniata, SusquehannBoulder Creek, Colorado, Boulder Creek Watershed, North Carolina
|
Stream, Surface-water, wastewater plant effluents
|
(Zabrecky et al., 2021), (Verplanck et al., 2005),(Verplanck et al., 2005) (Johannesson et al., 2000),(Verplanck et al., 2010),(Bau et al., 2006),(Rogosnitzky & Branch, 2016)
|
Benin
|
Africa
|
N/A
|
Cotonou,
|
Wastewaters, well water
|
(Atinkpahoun et al., 2020)
|
|
France
|
Europe
|
15.43
|
Hérault, Garonne, Bordeaux, Lorraine, Moselle, Southern France
|
Wastewaters, Surface Waters, rivers, Marine waters
|
(M. Rabiet et al., 2009);(Parant et al., 2018)
|
|
Japan
|
Asia
|
55.21
|
Nagoya, Hokkaido, Tokyo, Japanese Ara, Tama, and Tone river-estuaries, Osaka Bay area
|
Seawater, River water, treated effluent.
|
(Ridley,2020),(Inoue et al., 2020) (Zhu et al., 2004), (Bau et al., 2006),(Rapp, 2018),
|
|
Italy
|
Europe
|
28.73
|
Trento and Bolzano/Bozen
|
River Waters
|
(Peter Möller et al., 2003)
|
|
The U.K.
|
Europe
|
N/A
|
England, River Thames, Danube river, Rhine- Meuse Delta
|
Rivers and Tap water
|
(Kulaksiz & Bau, 2011a)
|
|
Belgium
|
Europe
|
11.61
|
Dommel in northern Belgium
|
Surface water, Groundwater
|
(Klaver et al., 2014);(Petelet-Giraud et al., 2009)
|
|
Netherlands
Czech
Republic
Switzerland
|
Europe
Europe
Europe
|
13.06
10.35
N/A
|
Dommel southern Netherlands
Prague, Eastern Bohemia region
across Switzerland
|
Surface water, Groundwater
Surface water, River, Sewage effluents Groundwaters.
wastewater treatment effluents
|
(Petelet-Giraud et al., 2009)
(P. Möller et al., 2002);(Bendakovská et al., 2016)
(Kaegi et al., 2021)
|
|
N/A= Not available
From the above Table 2, it can be observed that almost all known water sources, including surface waters (rivers, ocean, seawater, and stream), municipal water supplies, Groundwater, and steams, across the globe are reportedly contaminated with Gd anomaly. The list reported in this review is by no means exhaustive because the detection of Gd in the aquatic and sediment systems is ongoing research. The risk associated with each identified water source varies considerably, and different priority attention and treatment techniques may be required. Most of the reported Gd anomaly incidence is found in the river and surface water that are highly dynamic reservoirs of various wastewater effluents. However, considering the natural hydrological cycle, there is no gainsaying that there could be a knock-on-effect from one source to another as the water moves through different tributaries resulting in point and non-point sources of water pollution (Ahuja, 2019; Wu et al., 2019; Council, 1999; Sullivan et al., 2005; Sasakova et al., 2018). Gd in the municipal tap and well water in identified locations in the U.K., Benin, and Germany indicates the precariousness of the potential exposure of people living in these communities to drinking Gd contaminated water at least at low concentrations.
Technologies for GBCAs Remediation in water
It is evident from the preceding that anomaly Gd contamination in water systems is a global threat that requires urgent appropriate actions regardless of the prevailing controversies. This position was also collaborated by (Ebrahimi & Barbieri, 2019). Therefore, a search for an effective treatment for removing anomaly gadolinium in water is critical to protect abiotic and biotic elements in the ecosystems due to its high toxicity (Rogowska et al., 2018; Gwenzi et al., 2018). Literature has reported several techniques employed to recover free metallic Gd and GBCAs from different aqueous solutions. However, most of the works reported removing free Gd using different techniques rather than GBCAs, which is the most sough (El-Sofany, 2008; Li et al., 2015; Zheng et al., 2019). Separation of GBCAs from wastewater had received lesser attention probably because it is relatively easier to separate the free Gd from an aqueous solution than the complex GBCAs, which is more challenging to treat by conventional technique. Indeed, the dissociation constant, thermodynamics, and kinetic stability among GBCAs types (linear and macrocyclic) limit their separability behaviors (Rogowska et al., 2018; Runge, 2018). The different remediation techniques for GBCAs within the last two decades are presented in Table 3.
Table 3. Remediation Techniques for GBCAS in aqueous solutions.
Method
|
Medium
|
Target metal
|
Brand Name
|
Chelate type
|
Charge at pH 7
|
Efficiency
|
Ref.
|
|
Adsorption
|
Aqueous solution
|
GBCAs
|
Dotarem, Magnevist, Primovist
|
Macrocyclic
Linear
linear
|
Cationic
Cationic
Cationic
|
70 - 90 %
|
(Elizalde-González et al., 2017)
|
|
Ozonation
|
Wastewater
|
GBCAs
|
Gadovist,
Omniscan,
|
Macrocyclic
Linear
|
Neutral
Neutral
|
Insignificant
|
(Cyris et al., 2013)
|
|
Biological Filters
|
Freshwater
|
GBCAs
|
Magnevist
Omniscan,
Dotarem
|
Linear
Linear
Macrocyclic
|
Cationic
Neutral
Cationic
|
Insignificant
|
(Braun et al., 2018)
|
|
Membrane
|
Wastewater
|
GBCAs
|
N/S
|
N/S
|
N/S
|
99.85 %
|
(Michael G. Lawrence et al., 2010)
|
N/S = Not-specified
The reverse osmosis separation technique activated carbon adsorption process, biological filters, and Ozonation are popular techniques reportedly applied to remediate GBCAs in an aqueous solution with widely varying efficiencies. The adsorption process is a simple design, low cost, and effective method for treating and removing inorganic and organic contaminants in water and wastewater. Gadolinium chelates removal in wastewater and drinking water through activated carbon adsorption is generally considered ineffective due to its low absorption capacity (Cyris, 2013). However, Elizalde-González et al. (Elizalde-González et al., 2017) achieved an adsorption capacity of 70 - 90 % for selected GBCAs using three different optimized carbon samples (commercial activated carbon, activated carbon obtained from guava seeds, activated carbon obtained from avocado). The highest removal was achieved with the commercial carbon sample, followed closely by the Avocado carbon. According to the authors, the pH, and the number of functional groups on the carbon, specifically, the phenolic functional groups, played a significant role in the removal efficiency. Unfortunately, its efficiency was dramatically reduced when model urine was treated, an observation attributed to the competing urine components, limiting the adsorption capacity. The limitation in the adsorption techniques is that its efficiency varies with Sorbent's types and the aqueous solutions' characteristic nature. Most of the sorbents are only effective for removing free Gd rather than the GBCAs except for the limited success reported by Elizalde-González et al. The observed limitation is attributable to the problem of fouling caused by other molecules present in the urine. Fouling is a common problem in the adsorption process that causes a significant decrease in the adsorption capacities of Sorbent; therefore, further research is required to tackle this gap.
Due to its solubility and chemical reactivity, the ozonation technique is strongly reactive and selective in water pollution control. The technique effectively inactivates micro-organisms and decomposes organic pollutants in water and wastewater treatment (Wei et al., 2017). Therefore, Cyris et al. determined the reactions of gadolinium chelates with ozone for Magnevist, Omiscan, and Gadovist chelates and obtained rate constants values of 4.8 ± 0.88, 46 ± 2.5, and 24 ± 1.5 M−1s−1, respectively. The values obtained for each chelate test show that the ozonation degradation of Gd chelates in wastewater is both slow and ineffective, and the techniques concluded to be unsuccessful (Cyris et al., 2013). Braun et al. (Braun et al., 2018) also attempted to use aquatic plants as biological filters to remove common GBCA- s (Omniscan and Dotarem) from water. Unfortunately, the test results strangely showed that none of the four investigated macrophytes (Elodea nuttallii, Lemna gibba, Ceratophyllum demersum, E., and Canadensis) had a remarkable impact on Gd removal even though biofilters have been effectively used to treat domestic and industrial wastewater to remove contaminants (Mulay & Rajasekhara Reddy, 2019). Curiously, the four investigated macrophytes show high bioaccumulation removal activity for other heavy metals like Pb, Ni, Mn, Cr, and Cd, indicating the peculiar separation behaviors of GBCAs.
The membrane separation is a favorite water treatment technology for removing pollutants from water and wastewater streams for re-use through a selectively permeable barrier. The barrier is usually a thin sheet of material separating substances based on their chemical and physical characteristics under a driving force (Brose et al., 2002; Ezugbe and Rathilal, 2020). The membrane technology's aims to produce high mechanical strength materials and an excellent and high degree of selectivity of the desired permeate, which comes in different modules including; Membrane filtration that is pressure-driven processes (microfiltration, ultrafiltration, nanofiltration, and reverse osmosis), Pressure and thermal Driven Processes (Membrane distillation), Non-pressure driven process (Forward Osmosis, Liquid membrane) and Non-pressure electricity-driven processes electrodialysis (Shen, 2016; Khanzada et al., 2020; Ezugbe and Rathilal, 2020; Wenten, 2015; Iritani and Katagiri, 2016; Mulder, 1991). The reverse osmosis has been demonstrated to be an effective technique to remove stable anthropogenic GBCAs contaminants from wastewater, preferably when employed at the last treatment stage (Brünjes and Hofmann, 2020; Thomsen, 2017; Schmidt et al., 2019). For instance, 99.85 % GBCAs removal efficiency was achieved with reverse osmosis in a state-of-the-art water treatment plant (Michael G. Lawrence et al., 2010). Thus, Reverse Osmosis is the only recognized technique among all the reported tested techniques that have proven efficient in removing the GBCAS. Unfortunately, it is a very costly option, primarily due to the high pressure required for its operation (Ezugbe and Rathilal, 2020; Crini and Lichtfouse, 2019; Ezugbe and Rathilal, 2020). The high cost of the reverse osmosis limits its practical inclusion in every treatment plant where it is required. Similarly, Jiang et al. opined that technological innovation and development of new components in the future are required to circumvent the identified limitations of reverse osmosis (Jiang et al., 2018). Hence further research is required to explore effective optional techniques to treat the anomaly Gd in water using a more affordable technique.