## 4 Discussion
### Soil Lead
#### 4.2.3 Lead Uptake in Radish
This may be an important factor for gardeners in determining which crops to grow in potentially Pb contaminated soil or in managing safe daily consumption levels of home-grown vegetables. Radishes grown in COMP demonstrated the greatest capacity for Pb translocation to shoots, followed by BIOC. Translocation is influenced by many factors, including species, physiological factors, and characteristics of individual metals, and is also known to increase in the presence of organic chelators like EDTA and DTPA [9; 53]. In astudy on Pb uptake by _Brassica campestris_ L., (pak choi cabbage) after treatment with green waste compost applied at 2%, 5%, and 10% (_w/w_), [PERSON] et al. (2020) suggest that humic and fulvic acids decomposed from compost played a role as chelators to form Pb complexes, which influenced translocation in tissues. Our data seem to support these findings ([PERSON] et al., 2020). High Pb concentrations are also known to destroy the physical barrier formed by the Casparian strip ([PERSON] et al., 2020). Low chlorophyll concentrations in plants grown in BIOC were likely not directly linked to Pb uptake given the low tissue Pb status relative to COMP and INF, but could point to the early onset of N deficiency. Radish and lettuce samples both displayed symptoms often associated with Pb exposure, which included severe stunting, chlorosis, poor root development, and lowered rates of germination. However, it was not possible to discern whether the observations we observed, such as stunting, were caused by Pb exposure or a nutrient deficiency, which can be expressed similarly. High concentrations of heavy metals can also amplify existent nutrient deficiencies in calcareous soils by interfering with plant nutrient uptake and transportation. For example, Pb has been shown to reduce Fe\({}^{2+}\) concentrations in radial leaves (K  
respond differently, not only in terms of soil available Pb, but also in regard to differences in plant uptake. Amending potentially contaminated garden soils with biochar appears to be a reliable method to reduce the risk of Pb exposure among urban gardeners. Significant declines in both soil Pb availability and plant bioaccumulation (almost 20% and 11%, respectively) in native soils amended with biochar point to effective Pb immobilization and reduced uptake by plants. Not as effective as biochar, compost nonetheless reduces soil available Pb by 8% when planted to radish, although this may primarily be a reflection of removal through plant uptake. The observed 19% increase in tissue content of radish grown in soil amended with compost is of concern, however, particularly for those growing root crops. In contrast, the water-soluble inorganic fertilizer used in this study has a detrimental impact in all respects. Not only does it mobilize soil Pb by 11%, but it also enhances plant uptake and bioaccumulation in radish by as much as 40%. This is likely due to a lack of key chemical reactions (adsorption, complexation, and precipitation) largely associated with the presence of organic matter that are known to reduce soil Pb availability. Further, because the added nutrients are in an exclusively plant-available form, plants grown in soil treated with an inorganic fertilizer produce significantly greater biomass than those in an unnamed soil, increasing the amount of Pb deposited in plant tissues on a per plant basis. For these reasons, use of water-soluble inorganic fertilizer should be avoided in potentially Pb contaminated garden soils, especially those low in organic matter. Gardeners are encouraged to test their soils for contamination and carefully consider crop selection, avoiding root crops. When needed, they should apply biochar in combination with compost. This combination of treatments is recommended to overcome a potential for initial N deficiency induced by biochar, which is alleviated by compost. More information on remediation of garden contaminated soils should be broadly available to audiences interested converting open urban areas into garden spaces.