Medical and supplement products from hemp (Cannabis sativa L.) has been studied and produced with accelerating speed but the industry lacks clear regulation to the contaminant contents of the end products. One important class of contamination is heavy metals, which are innate ingredients of the earth’s crust and are classified as essential heavy metals, which include Fe, Mn, Co, Cr and Mo, which are important for biological processes \cite{Bhattacharya2016} and non-essentials include Hg, Pu, Cd and Pb \cite{Bhattacharya2016,Kumar_2017,Tchounwou2012}, which are harmful even at low concentrations \cite{Bhattacharya2016,Tchounwou2012}.
Other than natural processes \cite{ismail2013phytoremediation,jadia2008phytoremediation}, the concentration of heavy metals are increased in the soil by human activities such as using heavy metal containing fertilizers, pesticides \cite{Asgari2017,Feng_2017} and ash \cite{Nieminen_2005}. One of the biggest sources of heavy metal accumulation in the soil is phosphate fertilizers \cite{Bolan_2013,McPartland_2017}. Phosphate ions are considered to be the main carrier of heavy metal contaminants and specifically hydroponic fertilizers have been found to have the highest tendency for contamination \cite{karadjovn.d.}. Additionally different manures have been proven to be a source of heavy metal contamination \cite{Singani_2012}.
Over one-third of the global arable lands are contaminated with heavy metals \cite{Tripathi_2016}. More specifically in Austria, France, Hungary, Slovakia and Sweden there are some 200,000 heavy metal contaminated areas \cite{yadav2018mechanistic}.
The bio-availability of heavy metals can be affected by using different kinds of fertilizers\cite{Barrutia_2009,nwaichi2010phytoextraction,li2012effect} . This has been documented in studies with oat (Avena sativa L.), ryegrass (Lolium multiflorum L.), carrot (Daucus carota L.), spinach (Spinacia oleracea L.) \cite{he1994crop,he1994cropa} and barley (Hordeum vulgare L.\cite{singh1998cadmium} to name a few.
The ability to accumulate heavy metals can be enhanced by adding endophytes \cite{Citterio2005,Luo2012,Rajkumar_2008,Wu_2010} and plant growth hormones \cite{Hadi_2010,hernandez1996morphogenesis,lee1999effect,yasin1989response}, which is confirmed to increase the accumulation in hemp \cite{ahmad2015effective}. Heavy metal tolerance related genes are being researched for future genetic applications  \cite{Ahmad_2015}.
When plant accumulates heavy metals or other toxins into their tissues in higher density than the growing medium, it can be called hyperaccumulator (Baker and Brooks 1989). The hyperaccumulator potential of hemp began to be discovered in Institute of Bast Corps of Ukraine in 1998, where it was planted after Chernobyl nuclear power plant accident to remove contamination from the soil (Ahmad et al. 2016).
The translocation of these metals is important to understand as they can concentrate into edible products made from the plant (Abdelsalam et al. 2019). Most of the heavy metals are accumulated into the roots (Ahmad, Hadi, and Ali 2015; Ahmad et al. 2016; Citterio et al. 2003; Giovanardi et al. 2002; Shi et al. 2012; G. Shi and Cai 2009), though Cd and Zn are accumulated mostly into the shoots (Löser et al. 2002) or more specifically into the leaves (Arru et al. 2004; Eboh and Thomas 2005; Giovanardi et al. 2002; Linger et al. 2002). In contrast the fiber does not accumulate heavy metals (Linger et al. 2002). It has been shown that the translocation of heavy metals from roots to shoots increases with higher heavy metal concentrations in soil (Ahmad et al. 2016). The heavy metal concentrations are very different with different hemp cultivars (Shi et al. 2012).
In contrast to accumulation of heavy metals, hemp could be considered to be a Cd excluder (G. Shi and Cai 2009; G. R. Shi et al. 2009) as its translocation factor (TF), which is the ratio of shoot and root heavy metal concentration \(TF=\frac{Cd_{shoot}}{Cd_{root}}<1\) is smaller than one, i.e. Cd accumulates mostly into roots, which is suggested to be a property of excluder plants (Baker and Whiting 2002). This means a lower risk for Cd to concentrate into products for human consumption.
The accumulation of heavy metals directly into the inflorescence seems to be under a debate with no specific studies done on the subject. Most of the studies are analysing the leaves with inflorescences or just leaves but not inflorescences as such. On the other hand accumulation of heavy metals to the leaves, inflorescence is claimed not to accumulate heavy metals (Husain et al. 2019), but is claimed outside the study itself in an interview of the author (“Hemp Cleans Toxic Soil and Produces Clean CBD Flower, Study Finds” 2019). Meanwhile it is known that heavy metal stress increases the phenolics content (Ahmad, Hadi, and Ali 2015) and specificly cannabinoid content (Husain et al. 2019), its exploitation or ignoring can have severe consequenses for the users health.
Heavy metal accumulation in the body of the end user is a health concern as they can be toxic and carcinogenic. Especially cadmium, mercury, lead (arsenic and nickel) are dangerous heavy metals. The bioavailability of heavy metals depends on the route of administration. For example pyrolysis turns contaminants into toxic compounds (Sullivan, Elzinga, and Raber 2013). Respiratory administration is more bioavailable than digestion for mercury. When constant accumulated these toxic metals cause oxidative stress which produces ROS (Reactive oxygen species), cancers, teratogenesis, mutagenesis, immunological syndromes (Hédiji et al. 2015), anemia, cognitive decline, cardiovascular diseases (Iqbal 2012) as well as brain, nervous system (Sastre, Ritchie, and Hajji 2015), bone, skin and teeth (Luo et al. 2012) conditions.
The American Herbal Pharmacopoeia (AHP) has proposed limits for hemp product heavy metal concentrations as follows: As 10.0 µg/day, Cd 4.1 µg/day Pb 6.0 µg/day and Hg 2.0 µg/day (Upton et al. 2014).
Hemp inflorescence base products are trending worldwide as nutraceuticals and medicines but lack clear regulation. Hence the heavy metal and other contamination concentration of products vary significantly - there are multiple cases of products which have found to contain high concentrations of heavy metals. For example already in 1988 it was discovered that hemp grown in vulcanic soil in Hawai contained Hg per gram of inflorescence concentration of 440 ng/g (Siegel, Garnier, and Siegel 1988). And more recently an analysis was done in european markets revealing that many of them had traces of heavy metals and other contaminants (Duclos 2019). Furthermore some medical products have been found to contain possible As contamination (Combemale et al. 2005; Noël 2001). 
This preliminary review and study was done to define the amount of Cd, Hg, and Pb accumulation in NatureDry© lyophilized FINOLA®  hemp juice made from inflorescence and leaves, grown in fine-sandy moraine soil type in Central Finland and to clarify the different ratios of biomaterials extractable from the flowers. In order to better plan industrial production of hemp inflorescence juice products.
Mercury, cadmium and lead was chosen for the metal analyses because as they are some of the most commonly occuring metals in soil, they are propably accumulating to hemp.

Methods

The field experiment was done with hemp cultivar FINOLA® in open pollinated field, with males and females. The soil type was fine-sandy moraine with organic matter class being medium and pH 6.7. Soil cultivation included plowing, harrowing, adding Belor Standard NPKS 26-5-5(-2) 2019 fertilizer 280 kg/ha. Location was in 61°51'57.1"N 25°43'48.8"E in Jyväskylä, Finland. Sowing date for the field experiment was 20.5.2019. Harvest date for the samples were in 3.9.2019, plants had around 60% mature seed, male flowers were already dead and seed harvest was approaching in few weeks.
Samples were randomly gathered from the field by hand 3.9.2019 with scissors and were frozen in regular freezer to -19°C in vacuum sealed bags, with vacuum machine (OBH Nordica 7949 Supreme Food Sealer). Inflorescenses and leaves were juiced straight from freezer using a twin gear slow juicer Angel Juicer 7500 (Angel, n.d.) with fine strainer filter. Juice was frozen again in vacuum sealed bags to -19°C. Finally the juice was lyophilized with NatureDry© method at Lyotech Oy with in Helsinki.
Laboratory analyses for heavy metal concentrations were done by Eurofins WEJ Contaminants GmbH in Hamburg Germany laboratory. Cd and Pb analyses was made with mass spectrometry and ionisation by inductively coupled plasma (ICP-MS). For Hg analysis, reduction of Hg compounds to Hg with Tin(II)-Chloride, then analysis of Hg vapour with atomic absorption spectroscopy (AAS).