Different vegetables and fruits grow in different ways, they absorb different kinds of nutrients and chemicals based on what they need to grow. Some are even more susceptible to contaminants and chemicals due to their nature. This is why organic produce is preferred by most health conscious people, a return to the time when no synthetic fertilizer is used.
Since a vast majority of people specially in the US and Europe shift to organic produce, to a point that in 2014 the US the organic industry’s annual dollar gain was valued at 35.77 Billion dollars  and in Europe the organic market grew by 7.4% and the retail sales are valued at 24 Billion Euros . And by simply looking at these numbers we can clearly state that the trend for organic produce is really picking up.
Due to the price difference between commercial and organic food, some people still prefer to buy the cheaper commercial crops.
Though we can say that buying the commercial crops would be reasonable, recent studies say that there are certain fruits and vegetables that we must always buy organic. Here are five of them.
Apples are said to be the most contaminated produce, with studies stating that up to 98% of the more than 700 apple samples that were tested were contaminated and had traces of pesticides on the fruits themselves.  USDA also discovered that 5 unapproved pesticides were found on some apple samples as well. These were the reason that apples were on top of the Environmental Working Group’s Dirty Dozen in 2011 and 2015.  Though some tests show that some of these insecticides can be washed away by certain chemical washes, it will still be safer to buy organic apples and organic apple products, like apple juice.
In the 2016, The Dirty Dozen List by EWG ranked strawberries first to the most number of pesticides used and number of traces there is found on the fruit.  And a study back in 2011 stated that at least 90% of the samples were positive to pesticide residue.  One of which is Captan, which in a study by the US National Pesticide information Center, was proven to be able to cause the sample laboratory rats multiple tumors and is classified under B2 by the U.S. EPA which is a probable human carcinogen. 
Ranked 8 in this year’s Dirty Dozen by EWG, certain grape samples were found to have traces of Captan according to a study by Gilvydis et al. A study back in 2011 also found out that 90% of the grapes samples they had from the market showed to have trace chemicals from insecticides.
Ranked 12 in this year’s Dirty Dozen by the EWG , potatoes were found to have more pesticides per weight than most types of produce and crops on the market.  In a study of the USDA Pesticide Data Program it was found out that there are 35 Pesticide Residues found in potatoes. 6 or more of which are either known or probable Carcinogens and 6 are Developmental or Reproductive toxins which are bad or which have an adverse effect on babies. 
Ranked 10 in this year’s Dirty Dozen by the EWG , tomatoes like potatoes were found to use about 69 Pesticides  and of which 35 had Pesticide Residues, of which 3 were either known or probable carcinogens, and 3 are Developmental or Reproductive Toxins, and 12 were Suspected Hormone Disruptors. 
These are just 5 of the long list of fruits and vegetables that are susceptible to trace insecticide, pesticide, and fertilizer chemicals. And as EWG and various other research groups say, the easiest way to stay away from these pesticides is to buy organic, since organic fruits and vegetables do not use these kinds of chemicals.
 Organic in Europe, IFOAM-EU Group, http://www.ifoam-eu.org/en/what-we-do/organic-europe
 Apples Can Be Tainted With Pesticides – But You Still Need Your Fruits and Vegetables, Bryan Walsh, TIME, 13 June 2011
Apples Can Be Tainted With Pesticides—But You Still Need Your Fruits and Vegetables
 12 Organic Fruits and Vegetables You Should Always Buy Organic (2015 Edition), Heather McClees, 25 February 2015,
 Effect of handling and processing on pesticide residues in food-a review, Usha Bajwa and Kulwant Singh Sandhu, PMC, 26 August 2011, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3907644/
 21 Foods to Always Buy Organic (Even If You’re On a Budget!), Jess Barron, 7 August 2017, http://www.livestrong.com/slideshow/1004202-20-foods-always-buy-organic-even-youre-budget/#slide=7
 All 48 Fruits and Vegetables With Pesticide Residue Data, Environmental Working Group, 2016, https://www.ewg.org/foodnews/list.php#.WYj0gISGPIU
 Captan (General Fact Sheet), National Pesticide Information Center (NPIC), 2000, http://npic.orst.edu/factsheets/captangen.pdf
 Residues of captan and folpet in strawberries and grapes, Gilvydis DM Walters SM Spivak ES Hedblad RK, 1986, J Assoc Off Anal Chem, https://www.ncbi.nlm.nih.gov/pubmed/3771451
 Potatoes, What’s on my Food, Pesticide Action Network North America, http://www.whatsonmyfood.org/food.jsp?food=PO#f3
 U.S. organic sales post new record of $43.3 Billion in 2015. Press Releases. News. https://www.ota.com/news/press-releases/19031