Tuesday, November 22, 2016

Give Thanks to the Spiny Dogfish, Squalus acanthias. By Don Orth

We should be grateful for our many fishy blessings on Thanksgiving. The Spiny Dogfish Squalus acanthias plays many roles in our world. It may be a bloody nuisance for commercial fishermen, but Spiny Dogfish once provided abundant fish oil and vitamin A.  Today they are a substitute fish for fish n chips. Why the dogfish even has its name on a brewery.  Through history, the Spiny Dogfish has posed many challenges. To the Spiny Dogfish and those who helped to overcome the challenges, we give thanks. 

Spiny Dogfish is the representative of the cartilaginous fishes (Chondrichthyes) that is dissected in anatomy labs throughout the world. Each year biology majors and pre-med students are challenged in comparative vertebrate anatomy lab before advanced study in human anatomy.  Here students dissect the dogfish shark and begin to compare organ systems among the chordates. Students name structures and consider their functional adaptations.   At night they review and cram from 3-pound dissection guides, such as Wischnitzer (2006) or Fishbeck and Sebastiani  (2015).   
Dissection of Spiny Dogfish in process in Ichthyology Lab. Photo: DJ Orth
The body of the Spiny Dogfish is slim with a narrow pointed snout and asymmetrical caudal fin lobes. Spiny Dogfish are slate gray on the dorsal surface and sides, and have characteristic white spots and a white belly.  The irregular white spots are typical of younger fish and may be lacking on older individuals.  It has two widely separated dorsal fins and two sets of paired fins.  It lacks an anal fin – how do you explain that? Maybe God meant for Ichthyology Professors to have a little fun with student lab practicals?  "Label the anal fin on this specimen."
Squalus acanthias (female 678 mm TL) from Ebert et al. (2010)
Commercial fishers are challenged to harvest high-valued fishes without catching unpopular dogfish. Spiny Dogfish grow to 3.3 (males) to 4 feet (females) and adults school near the bottom where they overlap with many more valuable food fishes, such as cod, halibut, flounder, and sole. When these valuable groundfish were overfished in the late 1980’s (Buchsbaum et al. 2005), commercial fishermen targeted the larger female Spiny Dogfish, leading to overharvest.  Spiny Dogfish are not the first choice of fishermen, and are an impediment to harvesting groundfish, such as the Silver Hake (aka, whiting) Merluccius bilinearis.  Trawlers targeting whiting use a small mesh trawl with a raised footrope to avoid catching some unwanted bottom fishes. However, the Spiny Dogfish is still captured with this gear.  An excluder grate installed on the trawl net reduces the catch of Spiny Dogfish and subsequent handing time and harvests more of the target fish. 
Dogfish excluder grate on a hake trawl.   Photo from Chosid et al. (2012)
Surprisingly, the naming was another challenge. Carolus Linnaeus first named the Spiny Dogfish in 1758.  Since that time 24 other species of Squalus have been discovered and named. For example, in 1854, Charles Girard named the North Pacific Dogfish, Squalus suckleyi.  Like many other complex taxonomic issues, reasonable people may disagree until careful measurements of meristic and morphometric measurements and genetic data from representative samples are analyzed.  In 1960, the American Fisheries Society committee on names of fishes, grouped the disconnected North Pacific and Atlantic populations into a single species Squalus acanthias, ignoring the work of Girard. It took 50 years before Ebert et al. (2010) examined meristic, morphological, and molecular data and resurrected the endemic North Pacific Squalus suckleyi.  Consequently, there is some confusion around names used in previous literature.  Further, there are still many other species of Squalus that need to be evaluated in order to understand the phylogeny of the the dogfish genus, Squalus.

The common name, dogfish, has always been a challenge.  It just doesn't sound like a chef’s delicacy. The name, dogfish, was been used since the 15th century as fishermen observed them hunting in packs.   Dokefyche is a middle English word that combines “dog” and “fish.”   Cabinet makers in the 19th century used the skins of dogfish to polish hardwoods.  Livers were also used by tanneries. Fisheries still considered the dogfish a trash species in the mid 20th century. Harvest was used for livestock and pet feed or fish meal.  However, the liver is high in natural vitamin A and fisheries once harvested the dogfish and used the liver oil to derive vitamin A. 

Many years ago it was marketed as Flake, Grayfish, Cape Shark, Japanese Halibut, or Rock Salmon  Like all marine elasmobranchs, the Dogfish maintains osmotic balance with its external environment with a mixture of urea and trimethyl amine oxide (TMAO) in its blood stream.  Otherwise they would lose freshwater to the marine environment and be unable to function. So that urea thing may keep you from ever trying a Dogfish entrĂ©e. But do try it. Just remember Dogfish must be bled, gutted, and iced immediately after harvest to avoid the urea settling in the tissues.  Watch the cleaning video. Soon after death, bacteria can quickly convert the urea in their blood and tissue into ammonia.  Yuk!  The taste of ammonia is not appealing, in fact, it's a sign of kidney disease!  So prepare the dogfish correctly and even consider marinating dogfish in something slightly acidic.  The result will be another delectable dish, thanks to the Spiny Dogfish.

Spiny Dogfish, although once overfished in the Northwest Atlantic, are now the largest shark fishery in US. The Spiny Dogfish is often maligned by commercial and recreational fishers and its role is misunderstood.  Also, the leading edge of their dorsal spine is a big, white, needle-sharp spine, a formidable weapon capable of inflicting agonizing pain. Bigelow and Schroeder (1948) in Fishes of the Western Atlantic, wrote “from a practical aspect the spiny dog in the Western Atlantic is chiefly important because it is undoubtedly more destructive to gear and interferes more with fishing operations than does any other fish – shark or teleost.”    

Spiny Dogfish are opportunistic feeders, preying on what is locally abundant.  They feed primarily on crustaceans when young, and move on to comb jellies, jellyfish, squid, and fish as they get larger.  Consequently, they are blamed for competing with valuable groundfish for food. They also eat commercially valuable fishes, such as mackerel, herring, and squid.   Ctenophores (comb jellies)  have become more prevalent in diets of Spiny Dogfish between 1981 and 2000; this increase likely reflects increased abundance of ctenophores (Link and Ford 2006; Ford and Link 2014).  Spiny Dogfish are slow growing and there are many predators on the Spiny Dogfish, including the Cod, Red Hake, Goosefish, larger sharks, seals, and orcas.   Many fisheries management decisions today are still made without quantifying many of these key ecosystem interactions (Murawski 2000).

Although Spiny Dogfish are not the most desirable fish in the sea, there is high demand in the United Kingdom for Fish n Chips and in Germany for a Beer Garden Snack, called shillerlocken.   Shillerlocken should not to be confused with the pastry named after the same German poet. Schaumrollen, or Schillerlocken, is something my grandfather Orth made in his bakery each Christmas.  It’s ironic that Spiny Dogfish are now protected under EU fishing regulations to stop it being caught and sold with chips, but it is legal to sell it in the UK provided it has been caught outside the EU and imported. 
Spiny Dogfish becomes the fish in "Fish n Chips"  Photo by Alamy (Source)
Changing demands on the Spiny Dogfish led to historical fluctuations in abundance. It is clear now from their life history, that the Spiny Dogfish is vulnerable to rapid overharvest without controls on harvest. Spiny Dogfish are difficult to age.  Validation of methods for examining annual marks on the spines or vertebrae were only recently validated via radiocarbon dating (Campana et al. 2006).  
Annual rings on the spines of Spiny Dogfish (from Campana et al. 2006, left) and on sectioned and stained vertebra (from Bubley et al. 2012,  right)
Growth and maturity studies indicate slow growth, late maturity, and low fertility.  Spiny Dogfish are viviparous and the embryos, called pups, feed off their yolk sac until parturition. The gestation period is long and fertility is low; gestation is 18 to 22 months.  Therefore, females give birth every other years to between 2 and 15 pups (average: 6).  The maximum reported size is 117 cm (=46 inches) total length and maximum reported age is 40 years. 
Growth (left, Bubley et al. 2012) and maturity, as measured by the female gonadosomatic index, of Spiny Dogfish (right, Bubley et al. 2013)
Fisheries scientists estimate population size and the removals from targeted fisheries and discards from bycatch. Large trawls are used to estimate catch per swept area and population size.  However, the Spiny Dogfish school and often school just ahead of the trawls.  Therefore, discard mortality and abundance, derived from trawl surveys, are uncertain estimates  (Rago et al. 1998; Rago and Sosobee 2009).  Female fish dominate the harvest of Spiny Dogfish. Harvesting results in truncated size and age distributions, which further reduces population productivity. Consequently, catch limits were imposed on harvests in US waters starting in 2000. These regulations allowed the Northwest Atlantic stock of the Spiny Dogfish to rebuild (Rago and Sosobee 2011).  However, commercial interests lobby for increases in catch limits and stock assessments are updated periodically to inform future management actions.   Meanwhile, Spiny Dogfish stocks in the eastern Atlantic are dwindling, which puts demands on Spiny Dogfish populations from US fisheries.  So challenges will continue. 

Remember to give thanks to the following on this Thanksgiving Day:  the Spiny Dogfish in your comparative anatomy lab, Carolus Linnaeus for naming the Spiny Dogfish, modern taxonomists for getting the names right, inventors for the dogfish excluder grate, fisheries biologists for revealing the life history of Spiny Dogfish, population analysts for trying to get the population numbers right, and fisheries managers for acting to limit harvests and sustain fisheries.  

Bubley, W.J., J. Kneebone, J.A. Sulikowski, and P.C.W. Tsang. 2012. Reassessment of spiny dogfish Squalus acanthias age and growth using vertebrae and dorsal-fin spines.  Journal of Fish Biology 80:1300-1319.
Bubley, W.J., J.A. Sulikowski, D.M. Koester, and P.C.W. Tsang. 2013.  Using a multi-parameter approach to reassess maturity of spiny dogfish, Squalus acanthias, following increased fishing pressure in the western North Atlantic.  Fisheries Research 147:202-212.
Buchsbaum, R., J. Pederson, and W. E. Robinson, editors. 2005. The Decline of Fisheries Resources in New England: Evaluating the Impact of Overfishing, Contamination, and Habitat Degradation. MIT Sea Grant College Program Publication No. 05-5.  
Campana, S. E., C. Jones, G.A. McFarlane, and S. Myklevoll.   2006. Bomb dating and age validation using the spines of spiny dogfish (Squalus acanthias). Environmental Biology of Fishes 77, 327–336.
Chosid, D.M., M. Pol, M. Szymanski, F. Mirarchi, and A. Mirarchi. 2012.  Development and observations of a spiny dogfish Squalus acanthias reduction device in a raised footrope silver hake Merluccius bilinearis trawl.  Fisheries Research 114:66-75.
Dell'Apa, A., C.W. Bangley, and R.A. Rulifson. 2015. Who let the dogfish out? A review of management and socioeconomic aspects of spiny dogfish fisheries.  Reviews in Fish Biology and Fisheries  DOI: 10.1007/s11160-014-9379-1
Ebert, D.A., W.T. White, K.J. Goldman, L.J.V. Compagno, T.S. Daly-Engel, and R.D. Ward. 2010. Resurrection and redescription of Squalus suckleyi (Girard, 1854) from the North Pacific, with comments on the Squalus acanthias subgroup (Squaliformes: Squalidae). Zootaxa 2612, 22–40.  
Fishbeck, D.W., and A. Sebastiani. 2015. Comparative Anatomy: Manual of Vertebrate Dissection 3rd Edition. Morton Publishing Company, 576 pp. 
Ford, M.D., and J.S. Link. 2014. Bounds on biomass estimates and energetic consequences of Ctenophora in the Northeast U.S. Shelf ecosystem. International Journal of Oceanography http://dx.doi.org/10.1155/2014/851809
Link, J. S., and M. D. Ford. 2006.  Widespread and persistent increase of Ctenophora in the continental shelf ecosystem off NE USA. Marine Ecology Progress Series 320:153–159
Murawski, S. A. 2000.  Definitions of overfishing from an ecosystem perspective.  ICES Journal of Marine Science 57:649-658.
Rago, P.J., K.A. Sosebee, J.K.T. Brodziak, S.A. Murawski, and E.D. Anderson. 1998. Implications of recent increases in catches on the dynamics of Northwest Atlantic spiny dogfish (Squalus acanthias). Fisheries Research 39, 165–181.   
Rago, P. J. and K. A. Sosebee. 2009 The agony of recovery: Scientific challenges of Spiny Dogfish recovery programs. pp 343-372. In V. F. Gallucci, G. A. McFarlane and G. G. Bargman eds. Biology and Management of Dogfish Sharks. American Fisheries Society, Bethesda Maryland.
Rago, P. and K. Sosebee. 2011.  Update on the status of Spiny Dogfish in 2011and initial evaluation of alternative harvest strategies. Mid Atlantic Fishery Management Council Science and Statistical Committee 
Wischnitzer, S. 2006. Atlas and Dissection Guide for Comparative Anatomy 6th Edition. W.H. Freeman, 368 pp.

Thursday, November 3, 2016

Mosquitofish, the Wrong Answer for Mosquito Control, by Don Orth

Journalist and satirist, H. L. Mencken, once wrote that “For every complex problem, there is an answer that is clear, simple, and wrong.”  I have no doubt that he wrote something more complicated.   We simplified it.  That’s what we do – we search for a simple and painless solution.  Mosquito control is one of those complex problems.  Mosquitoes (family Culicidae) have the potential to transmit malaria, West Nile, Zika, dengue, chikungunya, yellow fever, and other pathogens. Mosquitoes are only one of several vectors involved and not all mosquitoes are alike.  The Asian Tiger Mosquito has spread to 36 states since appearing in the USA in 1985 (Rochlin et al. 2013).   Constant monitoring and control efforts are needed to prevent the spread of mosquito-borne diseases. Even your backyard water gardens get more controversial with rise of Zika virus and West Nile virus.       
Mosquito larvae.  Photo by Napat Polchoke via Getty Images. Source   
The simple control solution is to stock a fish that eats mosquito larvae.  It has been adopted time and time again since the early 1900s.  The first choice was Mosquitofish, Gambusia affinis.   Entomologist Leland O. Howard (1857-1950) was the first to advocate for the use of mosquitofish for mosquito control.  William Seal (1910) first transported mosquitofish from North Carolina to New Jersey for mosquito control.  At the same time, Gambusia affinis were transported to Hawaii, tested on mosquito eggs and larvae, and christened the “greatest mosquito killer in existence” by David Starr Jordan (1926).   From there it went all around the world to save lives threatened by mosquito-borne diseases.  Soon it had wider distribution than any other freshwater fish (Krumholz 1948; Pyke 2008).  The simple solution was widespread long before effectiveness trials were conclusive.

The mosquitofish solution to the problem was and continues to be “clear, simple, and wrong!” Yes, the mosquitofish are superbly adapted to eating mosquito larvae.  But the story is more complicated.   Gambusia are in the Family Poeciliidae, one of the most popular families of fishes used in scientific research.  Poeciliids are commonly referred to as guppies, swordtails, topminnows, and mosquitofish.   Gambusia occur over most of Central America, Mexico, the southeastern USA, and major islands of the Caribbean, where they are differentiated to adapt to desert rivers and springs, subtropical habitats, and marine islands.  Meffe and Snelson (2009) listed 45 extant species of Gambusia, yet only two are invasive.  These are the Eastern Mosquitofish Gambusia holbrooki and the Western Mosquitofish Gambusia affinis.    Click to view a photo of  Eastern Mosquitofish femaleWestern Mosquito fish femaleWestern Mosquitofish male.  The Genus name, Gambusia, was derived from the Cuban term, ‘Gambusino,’ which means "nothing", usually in the context of disappointment or scorn (Krumholz 1948). When an angler returns from fishing without any fish, Cubans reportedly say "been fishing for Gambusinos."
 Gambusia and mosquito larva in a simplified depiction. (Sholdt et al. 1972)
Two important life history traits of the Gambusia are viviparity (they bear live young) and the specialized body form designed for near-surface feeding. Louis Krumholz conducted the most thorough studies of Gambusia affinis in their native range, measuring and sexing 30,093 mosquitofish during the investigation. Young receive nutrition from the mother and incubation lasts 21-25 days.  Therefore, the young suffer low prenatal mortality. The young are precocious and live independent of the parents after birth. Number of offspring produced per female is influenced by female size; Krumholz (1948) counted 10 embryos from a 35 mm female and 315 from a 59 mm female.   Mosquitofish are reproductively active during the warm seasons of the year and females may produce live offspring up to 4 or 5 times per year (Krumholz 1948). Young mosquitofish may reach sexual maturity in under 4 weeks.  All these traits makes initial population growth after introduction explosive. 

Length (mm)  frequency of one sample of female mosquitofish, in July of 1939, from  Argonne Woods Pond, Cook County, Illinois.  Shaded bars represent gravid females. (Krumholz 1948).
Mosquitofish display aggressive behavior toward other fishes and rapidly colonize new habitats.  Males tend to be more aggressive than females and bite and nip at fish and amphibians. Mosquitofish are extreme habitat generalists and typically found along shallow margins of streams, ponds, and wetlands. The genetic variability in two common Gambusia species is among the highest found for vertebrates (Smith et al. 2009).   Furthermore, local populations are adapted to different conditions via drift and dispersal mechanisms.   Hence, widespread stocking is not a wise action.  

While they eat mosquitofish larvae, mosquitoes are not an exclusive food.  Hence, the failure of the clear and simple solution arises from the unfortunate side-effects.  The simple facts that they can consume 80% of their body weight each day or can eat between 71 and 463 mosquito larvae per day (Chipps and Wahl 2004) encourages continued interest in use of Gambusia for mosquito control. Under some circumstances mosquitofish control is moderate at best (Cech and Linden 1987; Bence 1988).   However, when mosquitoes are reduced, other mosquito predators will be eaten. If there is a heavy, matted growth of algae, larvae will be protected from mosquitofish. If the pond has zooplankton (and most do), consumption of mosquito larvae drops substantially as the mosquitofish feed on the cladocerans, ostracods, copepods (Bence 1988).  As a consequence of the flexible feeding of the mosquitofish, mosquito populations rebound after an initial reduction.   Further, the high consumptive food demand of the mosquitofish at warm temperatures leads to many problems with effects on non-target animals.  Marshall Laird, from the Memorial University of Newfoundland, in 1977, wrote: "Time has proved that mosquitofish eventually became harmful in some areas to which they were introduced half a century ago --- the harm ranged from eating the eggs of economically desirable fish, to endangering rare indigenous species.” (Laird 1977, p 336).  
Distribution maps of Gambusia affinis (left) and Gambusia holbrooki (right). Source USGS 
Eating mosquito larvae is one thing.  Controlling mosquito populations is quite another.   Ineffectiveness of mosquitofish for mosquito control has been cited by numerous authors.  In fact, in many cases the introduction of mosquitofish reduced or eliminated populations of native mosquito predators.  They may be named “mosquitofish” but their aggressive behavior means they will eat eggs and larvae of fish, insects, and amphibians.   Numerous trials have been done and many introductions of mosquitofish have occurred outside their native range.   The evidence continues to support Marshall Laird’s contention that mosquitofish eventually prove more harmful than good on all continents (Bence 1989; Arthington 1991; Rupp 1996; Arthington and Lloyd 2009; Courtney and Meffe 2009).  Numerous fish farms continue to sell live mosquitofish, even through Amazon.com.   Why are mosquitofish in use today?   Some states do not restrict them because they are native species. Elsewhere, mosquitofish still have public relations value.   

Do you have nuisance mosquitos to control?  Look to native fishes; in many trials native fish have proven more effective at reducing mosquito by eating their larvae.   Small sunfish and catfishes are natural mosquito predators. Locally, you can try Fathead Minnows Pimephales promelas (Irwin and Paskewitz 2009).  The name does not suggest it will be the greatest mosquito killer in existence.  But, the Fathead Minnow is widely distributed from the Rocky Mountains to the Appalachian Mountains.  You may use mosquitofish in closed container water gardens, but if there are other fish in your small ponds, you don’t want to add mosquitofish.

The search for a feasible and rational control method continues. Bacterial larvicides, such as Bacillus sphaericus Neide (VectoLex), are expensive alternatives. but Culex mosquitoes develop resistance after repeated applications.  Currently Miami Beach is asking the Food and Drug Administration for emergency permission to release genetically modified mosquitoes in response to emergence of the Zika virus.  Another innovation is the use of nanoparticles, e.g. silver nanoparticles, to reduce mosquito populations without detrimental effects of fishes (Subramaniam et al. 2015).   

My message is clear and simple. Do not introduce mosquitofish outside their native range. Use native fish for mosquito control.  For more information on mosquitos and mosquito control, consult the American Mosquito Control Association, or your county extension agent. 

Arthington, A. H. 1991. Ecological and genetic impacts of introduced and translocated freshwater fishes in Australia. Canadian Journal of Fisheries and Aquatic Sciences 48 (Suppl. 1): 33-43.
Arthington, A.H., and L.N. Lloyd. 2009.  Introduced Poeciliids in Australia and New Zealand.  Pages 333-348 in G.K. Meffe and F.F. Snelson, Jr., Editors. Ecology and evolution of livebearing fishes.  Prentice-Hall, Inc., Engelwood Cliffs, New Jersey.
Bence, J. R. 1988. Indirect effects and biological control of mosquitoes by mosquitofish. Journal of Applied Ecology 25:505-521.
Cech, J.J., Jr., and A.L. Linden. 1987.  Comparative larvivorous performance of mosquitofish, Gambusia affinis, and juvenile Sacramento blackfish, Orthodon microlepidotus, in experimental paddies.  Journal of the American Mosquito Control Association 3:35-41.
Chipps, S.R., and D.H. Wahl. 2004. Development and evaluation of a western mosquitofish bioenergetics model. Transactions of the American Fisheries Society 133 (5):1150-1162.
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Courtenay, W. R. & G. K. Meffe. 1989. Small fishes in strange places: a review of introduced poeciliids. Pp. 319-331, in: G. K. Meffe & F. F. Snelson (eds.), Ecology and evolution of livebearing fishes (Poeciliidae). Prentice Hall, New Jersey, 453 pp.
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Jordan, D.S. 1926. Malaria and the mosquitofish.  Scientific American 1926:296-297.
Krumholz, L. A. 1948.  Reproduction in the western mosquitofish, Gambusia affinis affinis (Baird & Girard) and its use in mosquito control.  Ecological Monographs 18:1-43.
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Smith, M.H., K.T. Scribner, J.D. Hernandez, and M.C. Wooten.  2009.  Demographic, spatial, and temporal genetic variation in Gambusia.  Pages 235-257 in G.K. Meffe and F.F. Snelson, Jr., Editors. Ecology and evolution of livebearing fishes.  Prentice-Hall, Inc., Engelwood Cliffs, New Jersey.
Subramaniam, J., and 16 coauthors.  20q5.  Eco-friendly control of malaria and arbovirus vectors using the mosquitofish Gambusia affinis and ultra-low dosages of Mimusops elengi-synthesized silver nanoparticles: towards an integrative approach?  Environmental Science Pollution Research 22:20067-20083.