The overall ratings of five chemicals stocks are down on Portfolio Grader this week. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, ICL-Israel Chemicals Ltd. (ICL) falls to a D (“sell”), worse than last week’s grade of C (“hold”). For more information, get Portfolio Grader’s complete analysis of ICL stock.

Tronox Ltd. (TROX) experiences a ratings drop this week, going from last week’s C to a D. Tronox produces and markets titanium dioxide. The stock gets F’s in Earnings Momentum, Equity and Sales Growth. To get an in-depth look at TROX, get Portfolio Grader’s complete analysis of TROX stock.

Marrone Bio Innovations, Inc. (MBII) ratings are on the decline this week as the company earns an F (“strong sell”). Last week, it received a D (“sell”). In Earnings Momentum, Equity, Cash Flow and Sales Growth the stock gets F’s. For more information, get Portfolio Grader’s complete analysis of MBII stock.

Flotek Industries, Inc. (FTK) is having a tough week. The company’s rating falls from a C to a D. Flotek manufactures and markets downhole equipment and specialty chemicals. As of Jan. 23, 2015, 12.2% of outstanding Flotek Industries, Inc. shares were held short. To get an in-depth look at FTK, get Portfolio Grader’s complete analysis of FTK stock.

Rentech Nitrogen Partners, L.P. (RNF) earns an F this week, falling from last week’s grade of D. Rentech Nitrogen Partners engages in the manufacture and sale of nitrogen fertilizer products for use in the United States. The stock gets F’s in Earnings Revisions, Cash Flow, Margin Growth and Sales Growth. For more information, get Portfolio Grader’s complete analysis of RNF stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.